System and method for operating a steam turbine with improved organization of logic and other functions in a sampled data control

ABSTRACT

The throttle and governor valves of a steam turbine are operated by a digital computer control system to provide speed and load control for the turbine. The computer includes a speed and load control which periodically generates control outputs and a separate logic control which responds to panel and contact inputs to generate logicals which structure the speed and load control. An analog scan periodically enters feedback parameters into the computer for use by the controls. An input contacts scan enters feedback logicals into the computer on demand, or under certain conditions periodically. A monitor operates with an auxiliary synchronizer to control the execution of the scans and the controls. The speed and load controls are bid for execution once each second to generate the control outputs which are applied to an external electrohydraulic control for the valves. The analog scan is bid for execution once each half second and the logic control is bid for execution on demand for performance of a logic function. The auxiliary synchronizer is bid for execution once each tenth of a second. The monitor controls the execution with a priority order of auxiliary synchronizer, speed and load control, analog scan and logic control. Certain logic and controller functions are performed commonly by a single programmed element as needed at different points in time by multiple parts of the controls.

This is a continuation of application Ser. No. 247,551 filed Apr. 26,1972, now abandoned.

CROSS-REFERENCE TO RELATED APPLICATIONS

1. Ser. No. 722,779, entitled "Improved System and Method for Operatinga Steam Turbine and an Electric Power Generating Plant" filed byTheodore C. Giras and Manfred Birnbaum on Apr. 4, 1968, assigned to thepresent assignee, and continued as Ser. No. 124,993 on Mar. 16, 1971,and Ser. No. 319,115, on Dec. 29, 1972.

2. Ser. No. 408,962, entitled "System and Method for Starting,Synchronizing and Operating a Steam Turbine with Digital ComputerControl" filed as a continuation of Ser. No. 247,877 which had beenfiled by Theodore C. Giras and Robert Uram on Apr. 26, 1972 and assignedto the present assignee and hereby incorporated by reference; otherrelated cases are set forth in Ser. No. 408,962.

BACKGROUND OF THE INVENTION

The present invention relates to steam turbine operating systems andmore particularly to sampled data turbine control systems which areorganized to provide more efficient and more flexible turbine operation.

In Ser. No. 319,115, there is generally disclosed a prior sampled datadigital computer control system for steam turbines in electric powerplants. In Ser. No. 408,962, there is disclosed a detailed computerembodiment of a sampled data turbine control system. The presentapplication has a disclosure like the latter patent application, and itis directed to certain features related to structural organization of asampled data control system not specifically disclosure in Ser. No.319,115 and not within the scope of Ser. No. 408,962.

The description of prior art herein is made on good faith and norepresentation is made that any prior art considered is the bestpertaining prior art nor that the interpretation placed on it isunrebuttable.

SUMMARY OF THE INVENTION

A system for operating a steam turbine includes an arrangement ofthrottle and governor valves and means for actuating the valves inaccordance with valve position signals. A digital controller is providedfor the turbine and means are provided for coupling turbine speed andload signals periodically to speed and load controls in the digitalcontroller to generate periodically valve position outputs for turbinespeed and load control. Means are provided for scanning contact signalinputs and turbine variable signal inputs for registration in thedigital controller. Preferably, a separate logic control is provided forgenerating mode control outputs in response to the signal inputs to thedigital controller, and the mode control outputs are applied to thespeed and load controls to provide for switching control elements in andout of the latter. The digital controller further includes means forgenerating synchronous outputs for triggering the operation of the speedand load controls on a periodic basis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram on an electric power plant including alarge steam turbine and a fossile fuel fired drum type boiler andcontrol devices which are all operable in accordance with the principlesof the invention;

FIG. 2 shows a schematic diagram on a programmed digital computercontrol system operable with a steam turbine and its associated devicesshown in FIG. 1 in accordance with the principles of the invention;

FIGS. 3A, 3B and 3C show a hydraulic system for supplying hydraulicfluid to valve actuators of the steam turbine;

FIG. 4 shows a simplified block diagram of the digital Electro HydraulicControl System in accordance with the principle of the invention;

FIG. 5 shows a block diagram of a control program used in accordancewith the principles of the invention;

FIG. 6 shows a block diagram of the programs and subroutines of thedigital Electro Hydraulic and the automatic turbine startup andmonitoring program in accordance with the principles of the invention;

FIG. 7 shows a table of program or task priority assignments inaccordance with the principles of the invention;

FIG. 8 shows the location of subroutines in accordance with theprinciples of the invention;

FIG. 9 shows a block diagram of a proportional-plus-reset controllerprogram which is operable in accordance with the principles of theinvention;

FIG. 10 shows a flow chart of the proportional-plus-reset subroutine(PRESET) which is operable in accordance with the principles of theinvention;

FIG. 11 shows a block diagram of a proportional controller function withdead band which is operable in accordance with the principles of theinvention;

FIG. 12 shows a flow chart of a speed loop (SPDLOOP) subroutine which isoperable in accordance with the principles of the invention;

FIG. 13 shows a block diagram of a subroutine for scanning contact closeinputs of the Digitial Electro Hydraulic System which is operable inaccordance with the principles of the invention; and

FIG. 14 shows a block diagram of an auxiliary synchronizer computerprogram which is operable in accordance with the principles of theinvention.

FIG. 15 shows a view of a part of an operator's control panel which isoperable in accordance with the principles of the invention;

FIG. 16 shows a view of a part of the operator's control panel which isoperable in accordance with the principles of the invention;

FIG. 17 shows a view of a portion of the operator's control panel whichis operable in accordance with the principles of the invention;

FIG. 18 is a block diagram of an analog scan system which is operable inaccordance with the principles of the invention;

FIG. 19 is a timing chart of the various programs and functions withinthe Digitial Electric Hydraulic System which is operable in accordancewith the principles of the invention;

FIG. 20 is a block diagram of conditions which cause initiation of alogic program which is operable in accordance with the principles of theinvention;

FIG. 21 is a simplified block diagram of a portion of the logic functionwhich is operable in accordance with the principles of the invention;

FIG. 22 is a block diagram of the logic program which is operable inaccordance with the principles of the invention;

FIG. 23 is a block diagram of a load control system which is operable inaccordance with the principles of the invention;

FIG. 24 is a flow chart of a breaker logic program which is operable inaccordance with the principles of the invention;

FIG. 25 is a block diagram of a megawatt feedback loop subroutine whichis operable in accordance with the principles of the invention;

FIG. 26 is a block diagram of an impulse pressure loop with a megawattloop in service which is operable in accordance with the principles ofthe invention;

FIG. 27 is a flow chart of an automatic synchronize logic program whichis operable in accordance with the principles of the invention;

FIG. 28 is a flow chart of an automatic dispatch logic program which isoperable in accordance with the principles of the invention;

FIG. 29 is a flow chart of an automatic turbine startup program which isoperable in accordance with the principles of the invention;

FIG. 30 is a flow chart of a remote transfer logic subroutine which isoperable in accordance with the principles of the invention;

FIG. 31 is a block diagram showing a panel task interaction functionwhich is operable in accordance with the principles of the invention;

FIG. 32 is a block diagram of a panel program which is operable inaccordance with the principles of the invention;

FIG. 33 is a block diagram showing a control task interface which isoperable in accordance with the principles of the invention;

FIG. 34 is a block diagram showing a control program which is operablein accordance with the principles of the invention;

FIG. 35 shows a block diagram of speed instrumentation and computationinterface with special speed sensing circuitry which is operable inaccordance with the principles of the invention;

FIG. 36 shows a block diagram of an operating mode selection functionwhich is operable in accordance with the principles of the invention;

FIGS. 37A and 37B show a flow chart of a select operating mode functionwhich is operable in accordance with the principles of the invention;

FIG. 38 shows a symbolic diagram of the use of a speed/load referencefunction which is operable in accordance with the principles of theinvention;

FIG. 39 is a block diagram showing a speed control function which isoperable in accordance with the principles of the invention;

FIG. 40 shows a block diagram of the load control system which isoperable in accordance with the principles of the invention;

FIG. 41 includes a flow chart of the load control system which isoperable in accordance with the principles of the invention;

FIG. 42 shows a block diagram of the throttle valve control functionwhich is operable in accordance with the principles of the invention;

FIG. 43 shows a mixed block diagram of a governor control functionprogram which is operable in accordance with the principles of theinvention;

FIG. 44 shows a block diagram of the Digital Electro Hydraulic Systemwhich is operable in accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A. POWER PLANT

More specifically, there is shown in FIG. 1 a large single reheat steamturbine constructed in a well known manner and operated and controlledin an electric power plant 12 in accordance with the principles of theinvention. As will become more evident through this description, othertypes of steam turbines can also be controlled in accordance with theprinciples of the invention and particularly in accordance with thebroader aspects of the invention. The generalized electric power plantshown in FIG. 1 and the more general aspects of the computer controlsystem to be described in connection with FIG. 2 are like thosedisclosed in the aforementioned Giras and Birnbaum patent applicationSer. No. 319,115. As already indicated, the present application isdirected to general improvements in turbine operation and control aswell as more specific improvements related to digital computer operationand control of turbines.

The turbine 10 is provided with a single output shaft 14 which drives aconventional large alternating current generator 16 to producethree-phase electric power (or any other phase electric power) asmeasured by a conventional power detector 18 which measures the rate offlow of electric energy. Typically, the generator 16 is connectedthrough one or more breakers 17 per phase to a large electric powernetwork and when so connected causes the turbo-generator arrangement tooperate at synchronous speed under steady state conditions. Undertransient electric load change conditions, system frequency may beaffected and conforming turbo-generator speed changes would result. Atsynchronism, power contribution of the generator 16 to the network isnormally determined by the turbine steam flow which in this instance issupplied to the turbine 10 at substantially constant throttle pressure.

In this case, the turbine 10 is of the multistage axial flow type andincludes a high pressure section 20, an intermediate pressure section22, and a low pressure section 24. Each of these turbine sections mayinclude a plurality of expansion stages provided by stationary vanes andan interacting bladed rotor connected to the shaft 14. In otherapplications, turbines operating in accordance with the presentinvention may have other forms with more or fewer sections tandemlyconnected to one shaft or compoundly coupled to more than one shaft.

The constant throttle pressure steam for driving the turbine 10 isdeveloped by a steam generating system 26 which is provided in the formof a conventional drum type boiler operated by fossil fuel such aspulverized coal or natural gas. From a generalized standpoint, thepresent invention can also be applied to steam turbines associated withother types of steam generating systems such as nuclear reactor or oncethrough boiler systems.

The turbine 10 in this instance is of the plural inlet front end type,and steam flow is accordingly directed to the turbine steam chest (notspecifically indicated) through four throttle inlet valves TV1-TV4.Generally, the plural inlet type and other front end turbine types suchas the single ended type or the end bar lift type may involve differentnumbers and/or arrangements of valves.

Steam is directed from the admission steam chest to the first highpressure section expansion stage through eight governor inlet valvesGV1-GV8 which are arranged to supply steam to inlets arcuately spacedabout the turbine high pressure casing to constitute a somewhat typicalgovernor valving arrangement for large fossil fuel turbines. Nuclearturbines might on the other hand typically utilize only four governorvalves.

During start-up, the governor valves GV1-GV8 are typically all fullyopened and steam flow control is provided by a full arc throttle valveoperation. At some point in the start-up process, transfer is made fromfull arc throttle valve control to full arc governor valve controlbecause of throttling energy losses and/or throttling controlcapability. Upon transfer the throttle valves TV1 TV4 are fully opened,and the governor valves GV1-GV8 are normally operated in the singlevalve mode. Subsequently, the governor valves may be individuallyoperated in a predetermined sequence usually directed to achievingthermal balance on the rotor and reduced rotor blade stressing whileproducing the desired turbine speed and/or load operating level. Forexample, in a typical governor valve control mode, governor valvesGV5-GV8 may be initially closed as the governor valves GV1-GV4 arejointly operated from time to time to define positions producing thedesired corresponding total steam flows. After the governor valvesGV1-GV4 have reached the end of their control region, i.e., upon beingfully opened, or at some overlap point prior to reaching the fullyopened position, the remaining governor valves GV5-GV8 are sequentiallyplaced in operation in numerical order to produce continued steam flowcontrol at higher steam flow levels. This governor valve sequence ofoperation is based on the assumption that the governor valve controlledinlets are arcuately spaced about the 360° periphery of the turbine highpressure casing and that they are numbered consecutively around theperiphery so that the inlets corresponding to the governor valves GV1and GV8 are arcuately adjacent to each other.

After the steam has crossed past the first stage impulse blading to thefirst stage reaction blading of the high pressure section, it isdirected to a reheater system 28 which is associated with a boiler orsteam generating system 26. In practice, the reheater system 28 maytypically include a pair of parallel connected reheaters coupled to theboiler 26 in heat transfer relation as indicated by the referencecharacter 29 and associated with opposite sides of the turbine casing.

With a raised enthalpy level, the reheated steam flows from the reheatersystem 28 through the intermediate pressure turbine section 22 and thelow pressure turbine section 24. From the latter, the vitiated steam isexhausted to a condenser 32 from which water flow is directed (notindicated) back to the boiler 26.

Respective hydraulically operated throttle valve actuators indicated bythe reference character 42 are provided for the four throttle valvesTV1-TV4. Similarly, respective hydraulically operated governor valveactuators indicated by the reference character 44 are provided for theeight governor valves GV1-GV8. Hydraulically operated actuatorsindicated by the reference characters 46 and 48 are provided for thereheat stop and interceptor valves SV and IV. A computer monitored highpressure fluid supply 50 provides for controlling fluid actuatoroperation of the valves TV1-TV4, GV1-GV8, SV and IV. A computersupervised lubricating oil system (not shown) is separately provided forturbine plant lubricating requirements.

The respective actuators 42, 44, 46 and 48 are of conventionalconstruction, and the inlet valve actuators 42 and 44 are operated byrespective stabilizing position controls indicated by the referencecharacters 50 and 52. If desired, the interceptor valve actuators 48 canalso be operated by a position control 56 although such control is notemployed in the present detailed embodiment of the invention. Eachposition control includes a conventional analog controller (not shown inFIG. 1) which drives a suitably known actuator servo valve (notindicated) in the well known manner. The reheat stop valve actuators 46are fully open unless the conventional trip system or other operatingmeans causes them to close and stops the reheat steam flow.

Since the turbine power is proportional to steam flow under the assumedcontrol condition of substantially constant throttle pressure, steamvalve positions are controlled to produce control over steam flow as anintermediate variable and over turbine speed and/or load as an endcontrol variable or variables. Actuator operation provides the steamvalve positioning, and respective valve position detectors PDT1-PDT4,PDG1-PDG8 and PDI are provided to generate respective valve positionfeedback signals for developing position error signals to be applied tothe respective position controls 50, 52 and 56. One or more contactsensors CSS provides status data for the stop valving SV. The positiondetectors are provided in suitable conventional form, for example, theymay make conventional use of linear variable differential transformeroperation in generating negative position feedback signals for algebraicsumming with respect to position setpoint signals SP in developing therespective input error signals. Position controlled operation of theinterceptor valving IV would typically be provided only under a reheatsteam flow cutback requirement.

A speed detector 58 is provided for determining the turbine shaft speedfor speed control and for frequency participation control purposes. Thespeed detector 58 can for example be in the form of a reluctance pickup(not shown) magnetically coupled to a notched wheel (not shown) on theturbo-generator shaft 14. In the detailed embodiment subsequentlydescribed herein, a plurality of sensors are employed for speeddetection. Analog and/or pulse signals produced by the speed detector58, the electric power detector 18, the pressure detectors 38 and 40,the valve position detectors PDT1-PDT4, PDG1-PDG8 and PDI, the statuscontact or contacts CSS, and other sensors (not shown) and statuscontacts (not shown) are employed in programmed computer operation ofthe turbine 10 for various purposes including controlling turbineperformance on an on-line real time basis and further includingmonitoring, sequencing, supervising, alarming, displaying and logging.

B. DEH - COMPUTER CONTROL SYSTEM

As generally illustrated in FIG. 2, a Digital Electro-Hydraulic controlsystem (DEH) 1100 includes a programmed digital computer 210 to operatethe turbine 10 and the plant 12 with improved performance and operatingcharacteristics. The computer 210 can include conventional hardwareincluding a central processor 212 and a memory 214. The digital computer210 and its associated input/output interfacing equipment is a suitabledigital computer system such as that sold by Westinghouse ElectricCorporation under the trade name of P2000. In cases when the steamgenerating system 26 as well as the turbine 10 are placed under computercontrol, use can be made of one or more P2000 computers or alternativelya larger computer system such as that sold by Xerox Data Systems andknown as the Sigma 5. Separate computers, such as P2000 computers, canbe employed for the respective steam generation and turbine controlfunctions in the controlled plant unit and interaction is achieved byinterconnecting the separate computers together through data links orother means.

The digital computer used in the DEH control system 1100 is a P2000computer which is designed for real time process control applications.The P2000 typically uses a 16 bit word length with 2's complement, asingle address and fixed word length operated in a parallel mode. Allthe basic DEH system functions are performed with a 16,000 word (16K), 3microsecond magnetic core memory. The integral magnetic core memory canbe expanded to 65,000 words (65K).

The equipment interfacing with the computer 210 includes a contactinterrupt system 124 which scans contacts representing the status ofvarious plant and equipment conditions in plant wiring 1126. The statuscontacts might typically be contacts of mercury wetted relays (notshown) which operate by energization circuits (not shown) capable ofsensing the predetermined conditions associated with the various systemdevices. Data from status contacts is used in interlock logicfunctioning and control for other programs, protection analog systemfunctioning, programmed monitoring and logging and demand logging, etc.

Operator's panel buttons 1130 transmit digital information to thecomputer 2010. The operator's panel buttons 1130 can set a loadreference, a pulse pressure, megawatt output, speed, etc.

In addition, interfacing with plant instrumentation 1118 is provided byan analog input system 1116. The analog input system 1116 samples analogsignals at a predetermined rate from predetermined input channels andconverts the signals sampled to digital values for entry into thecomputer 210. The analog signals sensed in the plant instrumentation1118 represent parameters including the impulse chamber pressure, themegawatt power, the valve positions of the throttle valves TV1 throughTV4 and the governor valves GV1 through GV8 and the interceptor valveIV, throttle pressure, steam flow, various steam temperatures,miscellaneous equipment operating temperature, generator hydrogencooling pressure and temperature, etc. A detailed list of all parametersis provided in Appendix 1. Such parameters include process parameterswhich are sensed or controlled in the process (turbine or plant) andother variables which are defined for use in the programmed computeroperation. Interfacing from external systems such as an automaticdispatch system is controlled through the operator's panel buttons 1130.

A conventional programmer's console and tape reader 218 is provided forvarious purposes including program entry into the central processor 212and the memory 214 thereof. A logging typewriter 1146 is provided forlogging printouts of various monitored parameters as well as alarmsgenerated by an automatic turbine startup system (ATS) which includesprogram system blocks 1140, 1142, 1144 (FIG. 6) in the DEH controlsystem 1100. A trend recorder 1147 continuously records predeterminedparameters of the system. An interrupt system 124 is provided forcontrolling the input and output transfer of information between thedigital computer 210 and the input/output equipment. The digitalcomputer 210 acts on interrupt from the interrupt system 124 inaccordance with an executive program. Interrupt signals from theinterrupt system 124 stop the digital computer 210 by interrupting aprogram in operation. The interrupt signals are serviced immediately.

Output interfacing is provided by contacts 1128 for the computer 210.The contacts 1128 operate status display lamps, and they operate inconjunction with a conventional analog/output system and a valveposition control output system comprising a throttle valve controlsystem 220 and a governor valve control system 222. A manual controlsystem is coupled to the valve position control output system 220 and isoperable therewith to provide manual turbine control during computershut-down. The throttle and governor valve control systems 220 and 222correspond to the valve position controls 50 and 52 and the actuators 42and 44 in FIG. 1. Generally, the manual control system is similar tothose disclosed in prior U.S. Pat. No. 3,552,872 by T. Giras et al andU.S. Pat. No. 3,741,246 by A. Braytenbah, both assigned to the presentassignee.

Digital output data from the computer 210 is first converted to analogsignals in the analog output system 224 and then transmitted to thevalve control system 220 and 222. Analog signals are also applied toauxiliary devices and systems, not shown, and interceptor valve systems,not shown.

C. SUBSYSTEMS EXTERNAL TO THE DEH COMPUTER

Making reference now to FIGS. 3A-3C, a hardwired digital/analog systemforms a part of the DEH control system 1100 (FIG. 2). Structurally, itembraces elements which are included in the blocks 50, 52, 42 and 44 ofFIG. 1 as well as additional elements. A hybrid interface 510 isincluded as a part of the hardwired system. The hybrid interface 510 isconnected to actuator system servoamplifiers 414 for the various steamvalves which in turn are connected to a manual controller 516, anoverspeed protection controller, now shown, and redundant DC powersupplies, not shown.

A controller shown in FIG. 3A is employed for throttle valve TV1-TV4control in the TV control system 50 of FIG. 1. The governor valvesGV1-GV8 are controlled in an analogous fashion by the GV control system52.

While the steam turbine is controlled by the digital computer 210, thehardwired system 511 tracks single valve analog outputs 520 from thedigital computer 210. A comparator 518 compares a signal from adigital-to-analog converter 522 of the manual system with the signal 520from the digital computer 210. A signal from the comparator 518 controlsa logic system 524 such that the logic system 524 runs an up-downcounter 526 to the point where the output of the converter 522 is equalto the output signal 520 from the digital computer 210. Should thehardwired system 511 fail to track the signal 520 from the digitalcomputer 210 a monitor light will flash on the operator's panel.

When the DEH control system reverts to the control of the backup manualcontroller 516 as a result of an operator selection or due to acontingency condition, such as loss of power on the automatic digitalcomputer 210, or a stoppage of a function in the digital computer 210,or a loss of a speed channel in the wide range speed control all asdescribed in greater detail infra, the input of the valve actuationsystem 322 is switched by switches 528 from the automatic controllers inthe blocks 50, 52 (FIG. 1) or 220, 222 (FIG. 2) to the control of themanual controller 516. Bumpless transfer is thereby accomplished betweenthe digital computer 210 and the manual controller 516.

Similarly, tracking is provided in the computer 210 for switchingbumplessly from manual to automatic turbine control. As previouslyindicated, the presently disclosed hybrid structural arrangement ofsoftware and hardware elements is the preferred arrangement for theprovision of improved turbine and plant operation and control withbackup capability. However, other hybrid arrangements can be implementedwithin the field of application of the invention.

D. DEH PROGRAM SYSTEM DEH Program System Organization, DEH Control LoopsAnd Control Task Program

With reference now to FIG. 4, an overall generalized control system ofthis invention is shown in block diagram form. The digitalelectrohydraulic (DEH) control system 1100 operates valve actuators 1012for the turbine 10. The digital electrohydraulic control system 1100comprises a digital computer 1014, corresponding to the digital computer210 in FIG. 2, and it is interconnected with a hardwired analog backupcontrol system 1016. The digital computer 1014 and the backup controlsystem 1016 are connected to an electronic servo system 1018corresponding to blocks 220 and 222, in FIG. 2. The digital computercontrol system 1014 and the analog backup system 1016 track each otherduring turbine operations in the event it becomes necessary or desirableto make a bumpless transfer of control from a digital computercontrolled automatic mode of operation to a manual analog backup mode orfrom the manual mode to the digital automatic mode.

In order to provide plant and turbine monitor and control functions andto provide operator interface functions, the DEH computer 1014 isprogrammed with a system of task and task support programs. The programsystem is organized efficiently and economically to achieve the endoperating functions. Control functions are achieved by control loopswhich structurally include both hardware and software elements, with thesoftware elements being included in the computer program system.Elements of the program system are considered herein to a level ofdetail sufficient to reach an understanding of the invention. Morefunctional detail in various programs is presented in Appendix 2.Further, a detailed listing of a DEH system program substantiallyconforming to the description presented herein is presented in Appendix3 in symbolic and machine language. Most of the listing is compiled by aP2000 compiler from instructions written in Fortran IV. A detaileddictionary of system parameters is presented in Appendix 1, and adetailed computer input/output signal list is presented in Appendix 4.Appendix 5 mainly provides additional hardware information related tothe hardwired system previously considered as part of the DEH controlsystem.

As previously discussed, a primary function of the digitalelectrohydraulic (DEH) system 1100 is to automatically position theturbine throttle valves TV1 through TV4 and the governor valves GV1through GV8 at all times to maintain turbine speed and/or load. Aspecial periodically executed program designated the CONTROL task isutilized by the P2000 computer along with other programs to be describedin greater detail subsequently herein.

With reference now to FIG. 5, a functional control loop diagram in itsperferred form includes the CONTROL task or program 1020 which isexecuted in the computer 1010. Inputs representing demand and rateprovide the desired turbine operating setpoints. The demand is typicallyeither the target speed in specified revolutions per minute of theturbine systems during startup or shutdown operations or the target loadin megawatts of electrical output to be produced by the generatingsystem 16 during load operations. The demand enters the block diagramconfiguration of FIG. 5 at the input 1050 of a compare block 1052.

The rate input either in specified RPM per minute or specified megawattsper minute, depending upon which input is to be used in the demandfunction, is applied to an integrator block 1054. The rate inputs in RPMand megawatts of loading per minute are established to limit the buildupof stresses in the rotor of the turbine-generator 10. An error output ofthe compare block 1052 is applied to the integrator block 1054. Ingenerating the error output the demand value is compared with areference corresponding to the present turbine operating setpoint in thecompare block 1052. The reference value is representative of thesetpoint RPM applied to the turbine system or the setpoint generatormegawatts output, depending upon whether the turbine generating systemis in the speed mode of operation or the load mode of operation. Theerror output is applied to the integrator 1054 so that a negative errordrives the integrator 1054 in one sense and a positive error drives itin the opposite sense. The polarity error normally drives the integrator1054 until the reference and the demand are equal or if desired untilthey bear some other predetermined relationship with each other. Therate input to the integrator 1054 varies the rate of integration, i.e.the rate at which the reference or the turbine operating setpoint movestoward the entered demand.

Demand and rate input signals can be entered by a human operator from akeyboard. Inputs for rate and demand can also be generated or selectedby automatic synchronizing equipment, by automatic dispatching systemequipment external to the computer, by another computer automaticturbine startup program or by a boiler control system. The inputs fordemand and rate in automatic synchronizing and boiler control modes arepreferably discrete pulses. However, time control pulse widths orcontinuous analog input signals may also be utilized. In the automaticstartup mode, the turbine acceleration is controlled as a function ofdetected turbine operating conditions including rotor thermal stress.Similarly, loading rate can be controlled as a function of detectedturbine operating conditions.

The output from the integrator 1054 is applied to a breaker decisionblock 1060. The breaker decision block 1060 checks the state of the maingenerator circuit breaker 17 and whether speed control or load controlis to be used. The breaker block 1060 them makes a decision as to theuse of the reference value. The decision made by the breaker block 1060is placed at the earliest possible point in the control task 1020thereby reducing computational time and subsequently the duty cyclerequired by the control task 1020. If the main generator circuit breaker17 is open whereby the turbine system is in wide range speed control thereference is applied to the compare block 1062 and compared with theactual turbine generator speed in a feedback type control loop. A speederror value from the compare block 1062 is fed to a proportional plusreset controller block 1068, to be described in greater detail laterherein. The proportional plus reset controller 1068 provides anintegrating function in the control task 1060 which reduces the speederror signal to zero. In the prior art, speed control systems limited toproportional controllers are unable to reduce a speed error signal tozero. During manual operation an offset in the required setpoint is nolonger required in order to maintain the turbine speed at apredetermined value. Great accuracy and precision of turbine speedwhereby the turbine speed is held within one RPM over tens of minutes isalso accomplished. The accuracy of speed is so high that the turbine 10can be manually synchronized to the power line without an externalsynchronizer typically required. An output from the proportional plusreset controller block 1068 is then processed for external actuation andpositioning of the appropriate throttle and/or governor valves.

If the main generator circuit breaker 17 is closed, the CONTROL task1020 advances from the breaker block 1060 to a summer 1072 where theREFERENCE acts as a feedforward setpoint in a combinedfeedforward-feedback load control system. If the main generator circuitbreaker 17 is closed, the turbine generator system 10 is being loaded bythe electrical network connected thereto.

In the control task 1020 of the DEH system 1100 utilizes the summer 1072to compare the reference value with the output of speed loop 1310 inorder to keep the speed correction independent of load. A multiplierfunction has a sensitivity to varying load which is objectionable in thespeed loop 1310.

During the load mode of operation the DEMAND represents the specifiedloading in MW of the generator 16 which is to be held at a predeterminedvalue by the DEH system 1100. However, the actual load will be modifiedby any deviations in system frequency in accordance with a predeterminedregulation value. To provide for frequency participation, a rated speedvalue in box 1074 is compared in box 1078 with a "two signal" speedvalue represented by box 1076. The two signal speed system provides highturbine operating reliability to be described infra herein. An outputfrom the compare function 1078 is fed through a function 1080 which issimilar to a proportional controller which converts the speed errorvalue in accordance with the regulation value. The speed error from theproportional controller 1080 is combined with the feedforward megawattreference, i.e., the speed error and the megawatt reference are summedin summation function or box 1072 to generate a combined speedcompensated reference signal.

The speed compensated load reference is compared with actual megawattsin a compare box or function 1082. The resultant error is then runthrough a proportional plus reset controller represented by program box1084 to generate a feedback megawatt trim.

The feedforward speed compensated reference is trimmed by the megawattfeedback error multiplicatively to correct load mismatch, i.e. they aremultiplied together in the feedforward turbine reference path bymultiplication function 1086. Multiplication is utilized as a safetyfeature such that if one signal e.g. MW should fail a large value wouldnot result which could cause an overspeed condition but instead the DEHsystem 1100 would switch to a manual mode. The resulting speedcompensated and megawatt trimmed reference serves as an impulse pressuresetpoint in an impulse pressure controller and it is compared with afeedback impulse chamber pressure representation from input 1088. Thedifference between the feedforward reference and the impulse pressure isdeveloped by a comparator function 1090, and the error output therefromfunctions in a feedback impulse pressure control loop. Thus, the impulsepressure error is applied to a proportional plus reset controllerfunction 1092.

During load control the megawatt loop comprising in blocks 1082 and 1084may be switched out of service leaving the speed loop 1310 and animpulse pressure loop operative in the DEH system 1100.

Impulse pressure responds very quickly to changes of load and steam flowand therefore provides a signal with minimum lag which smooths the inputresponse of the turbine generator 10 because the lag dynamics andsubsequent transient response is minimized. The impulse pressure inputmay be switched in and out from the compare function 1090. Analternative embodiment embracing feedforward control with impulsepressure feedback trim is applicable.

Between block 1092 and the governor valves GV1-GV8 a valvecharacterization function for the purpose of linearizing the response ofthe values is interposed. The valve characterization function describedin detail in Appendix III infra herein is utilized in both automaticmodes and manual modes of operation of the DEH system 1100. The outputof the proportional plus reset controller function 1092 is thenultimately coupled to the governor valves GV1-GV8 throughelectrohydraulic position control loops implemented by equipmentconsidered elsewhere herein. The proportional plus reset controlleroutput 1092 causes positioning of the governor valves GV1-GV8 in loadcontrol to achieve the desired megawatt demand while compensation ismade for speed, megawatt and impulse pressure deviations from desiredsetpoints.

Making reference to FIG. 6, the control program 1020 is shown withinterconnections to other programs in the program system employed in theDigital Electro Hydraulic (DEH) system 1100. The periodically executedprogram 1020 receives data from a logic task 1110 where mode and otherdecisions which affect the control program are made, a panel task 1112where operator inputs may be determined to affect the control program,an auxiliary synchronizer program 1114 and an analog scan program 1116which processes input process data. The analog scan task 1116 receivesdata from plant instrumentation 1118 external to the computer asconsidered elsewhere herein, in the form of pressures, temperatures,speeds, etc. and converts such data to proper form for use by otherprograms. Generally, the auxiliary synchronizer program 1114 measurestime for certain important events and it periodically bids or runs thecontrol and other programs. An extremely accurate clock function 1120operates through a monitor program 1122 to run the auxiliarysynchronizer program 1114.

The monitor program or executive package 1122 also provides forcontrolling certain input/output operations of the computer and, moregenerally, it schedules the use of the computer to the various programsin accordance with assigned priorities. For more detail on the P2000computer system and its executive package, reference is made to Appendix4. In the appendix description, the executive package is described asincluding analog scan and contact closure input routines, whereas theseroutines are considered as programs external to the executive package inthis part of the disclosure.

The logic task 1110 is fed from outputs of a contact interrupt orsequence of events program 1124 which monitors contact variables in thepower plant 1126. The contact parameters include those which representbreaker state, turbine auto stop, tripped/latched state interrogationdata states, etc. Bids from the interrupt program 1124 are registeredwith and queued for execution by the executive program 1111. The controlprogram 1110 also receives data from the panel task 1112 and transmitsdata to status lamps and output contacts 1128. The panel task 1112receives data instruction based on supervision signals from the operatorpanel buttons 1130 and transmits data to panel lamps 1132 and to thecontrol program 1020. The auxiliary synchronizer program 1114synchronizes through the executive program 111 the bidding of thecontrol program 1020, the analog scan program 1116, a visual displaytask 1134 and a flash task 1136. The visual display task transmits datato display windows 1138.

The control program 1020 receives numerical quantities representingprocess variables from the analog scan program 1116. As alreadygenerally considered, the control program 1020 utilizes the values ofthe various feedback variables including turbine speed, impulse pressureand megawatt output to calculate the position of the throttle valvesTV1-TV4 and governor valves GV1-GV8 in the turbine system 10, therebycontrolling the megawatt load and the speed of the turbine 10.

To interface the control and logic programs efficiently, the sequence ofevents program 1124 normally provides for the logic task 1110 contactstatus updating on demand rather than periodically. The logic task 1110computes all logical states according to predetermined conditions andtransmits this data to the control program 1020 where this informationis utilized in determining the positioning control action for thethrottle valves TV1-TV4, and the governor valves GV1-GV8. The logic task1110 also controls the state of various lamps and relay type contactoutputs in a predetermined manner.

Another important part of the DEH system is the OPERATOR'S PANELprogram. The operator communicates through the panel with the DEHcontrol programs by means of various buttons which have assignedfunctions. When any button is pressed, a special interrupt is generated;this interrupt triggers a PANEL INTERRUPT program which decodes thebutton pressed, and then bids the PANEL task. The PANEL programprocesses the button and takes the proper action, which usually meansmanipulating some panel lamps, as well as passing on the buttoninformation to both the LOGIC and the CONTROL tasks.

The Operator's Panel also has two sets of display windows which allowdisplay of all turbine program parameters, variables, and constants. Avisual display task presents this information in the windows at therequest of the operator through various dedicated display buttons and anumerical keyboard. The visual display values are periodically updatedin the windows as the quantity changes.

Certain important turbine operating conditions are communicated to theDEH operator by way of flashing lamps on the panel. Therefore a specialFLASH program is part of the DEH system. Its function is to monitor anddetect such contingency conditions, and flash the appropriate lamp toalert the operator to the state.

E. TASK PRIORITY ASSIGNMENTS

With reference now to FIG. 7, a table of program priority assignments isshown as employed in the executive monitor. A program with the highestpriority is run first under executive control if two or more programsare ready to run. The stop/initializer program function has top priorityand is run on startup of the computer or after the computer has beenshut down momentarily and is being restarted. The control program 1020is next in order of priority. The operator's panel program 1130, whichgenerates control data, follows the control task 1020 in priority. Theanalog scan program 1116 also provides information to the control task1020 and operates at a level of priority below that of the operator'spanel 1130. The automatic turbine starting (ATS) periodic program 1140is next in the priority list. ATS stands for automatic turbine startupand monitoring program, and is shown as a major task program 1140 ofFIG. 6 for the operation of the DEH system 1100. The ATS-periodicprogram 1140 monitors the various temperatures, pressures, breakerstates, rotational velocity, etc. during start-up and during loadoperation of the turbine system.

The logic task 1110, which generates control and operating mode data,follows in order of operating priority. The visual display task program1134 follows the logic task program 1110 and makes use of outputs fromthe latter. A data link program for transmitting data from the DEHsystem to an external computer follows. An ATS-analog conversion taskprogram 1142 for converting the parameters provided by the ATS-periodicprogram 1142 to usable computer data follows in order of priority. Theflash task program 1136 is next, and it is followed by a programmer'sconsole program which is used for maintenance testing and initialloading of data tapes. The next program is an ATS-message writer 1144which provides for printout of information from the ATS analogconversion program 1142 on a suitable typewriter 1146. The next programin the priority list is an analog/digital trend which monitorsparameters in the turbine system 10 and prints or plots them out foroperator perusal. The remaining two programs are for debugging andspecial applications.

In the preferred embodiment, the stop/initialize program is given thehighest priority in the table of FIG. 7 because certain initializingfunctions must be completed before the DEH system 1100 can run. Theauxiliary synchronizer program 1114 provides timing for all programsother than the stop/initialize program while the DEH system 1100 isrunning. Therefore, the auxiliary synchronizer task program 1400 has thesecond order of priority of the programs listed. The control program1020 follows at the third descending order of priority since thegovernor valves GV1 through GV8 and the throttle valves TV1 through TV4must be controlled at all times while the DEH system 1100 is inoperation.

The operator's panel program 1130 is given the next order of priority inorder to enable an operator to exercise direct and instantaneous controlof the DEH system 1100. The analog scan program 1116 provides input datafor the control program 1020 and, therefore, is subordinate only to theinitialize synchronizer control and operator function.

In the preferred embodiment the ATS-periodic program 1140 is next inorder of priority. During automatic turbine startup, the scanning ofinputs by the ATS-periodic program 1140 is almost on the same order ofpriority as the inputs to the DEH system 1100. However, the ATS program1140 in alternative embodiments, could be reduced in its priority,without any considerable adverse effect, because of the relativelylimited duty cycle problems in the ATS system.

The logic task 1110 which control the operations of some of thefunctions of the control task program 1020 is next in order of priority.The visual display task 1134 follows in order of priority in order toprovide an operator with a visual indication of the operation of the DEHprogram 1100. The visual display program 1134 is placed in therelatively low eighth descending order of priority since the physicalresponse of an operator is limited in speed to to 0.2 to 0.5 sec. as toa visual signal. The rest of the programs are in essentially descendingorder of importance in the preferred embodiment. In alternativeembodiments of the inventions, alternate priority assignments can beemployed for the described or similar programs, but the general prioritylisting described is preferred for the various reasons presented.

A series of interrupt programs interrupt the action of the computer andfunction outside the task priority assignments to process interrupts.One such program in FIG. 6 is the sequence events or contact interruptprogram 1124 which suspends the operation of the computer for a veryshort period of time to process an interrupt. Between the operator panelbuttons 1130 and the panel task program 1112 a panel interrupt program1156 is utilized for signalling any changes in the operator's panelbuttons 1130. A valve interrupt program 1158 is connected directlybetween the operator's panel buttons 1130 and the panel task program1112 for operation during a valve test or in case of valve contingencysituations.

Proportional plus reset controller subroutine 1154 FIG. 9 is called bythe control task program 1020 of FIG. 5 as previously described when theturbine control system is in the speed mode of control and also, forcomputer use efficiency, when the turbine 10 is in the load mode ofcontrol with the megawatt and impulse pressure feedback loops inservice. Utilizing the proportional plus reset function 1068 duringspeed control provides very accurate control of the angular velocity ofthe turbine system.

In addition to previously described functions, the auxiliarysynchronizer program 1114 is connected to and triggers the ATS periodicprogram 1140, the ATS analog conversion routine 1142 and the messagewriter 1144. The ATS program 1140 monitors a series of temperature,vibration, pressures, speed, etc. in the turbine system and alsocontains a routine for automatically starting the turbine system 10. TheATS analog conversion routine 1142 converts the digital computer signalsfrom the ATS periodic program 1140 to analog or digital or hybrid formwhich can be typed out through the message writer task 1144 to thelogging typewriter 1146 or a similar recorder.

The auxiliary synchronizer program 1114 also controls an analog/digitaltrend program 1148. The analog digital trend program 1148 records a setof variables in addition to the variables of the ATS periodic program1140.

Ancillary to a series of other programs is a plant CCI subroutine 1150where CCI stands for contact closure inputs. The plant CCI subroutine1150 responds to changes in the state of the plant contacts astransmitted over the plant wiring 1126. Generally, the plant contactsare monitored by the CCI subroutine 1150 only when a change in contactstate is detected. This scheme conserves computer duty cycle as comparedto periodic CCI monitoring. However, other triggers including operatordemand can be employed for a CCI scan.

As shown in FIG. 6, the control task 1020 calls ancillary thereto aspeed loop task 1152 and the preset or proportional plus resetcontroller program 1154. Ancillary to the executive monitoring program1122 is a task error program 1160. In conjunction with the clock program1120 a stop/initialize program 1162 is used. Various other functions inFIG. 6 are described in greater detail infra.

F. DEH PROGRAMS OR TASKS

Making reference now to FIG. 9, a functional diagram of the proportionalplus reset controller task program 1068 of FIG. 5 is shown in greaterdetail. The proportional plus reset controller subroutine 1068 is calledby the control program 1020 of FIG. 5 when the DEH turbine controlsystem 1100 is in the speed mode of control and also when the DEHturbine control system 1100 is in the load mode of control with themegawatt and impulse pressure feedback loops in service. As alreadyindicated utilizing a proportional plus reset function during speedcontrol provides very accurate control of the angular velocity of theturbine system.

The proportional plus reset controller 1068 provides an output which iscomposed of the sum of two parts. One part of the output is proportionalto an input and the other part is an integral of the input. Therefore,instantaneous response is available as well as the capability of zeroinput error. A setpoint or dynamic reference from a demand source isapplied to an input 1210 of a difference function 1212. The differencefunction 1212 compares the input and the actual controlled processvalue. An output from the difference function 1212 is fed to aproportional gain function 1216 and to an input of an integrator orintegrating function 1218 having a reset time TR. An output from theintegrator 1218 is high and low limited by the program as represented bythe reset windup prevention function 1220 in order to avoid excessiveintegrator outputs which could occur with a reset windup.

Proportional and integral outputs from the gain function 1216 and thewindup limited integrator 1218 are summed in a summing function 1222.The total output from the summing function 1222 is high and low limitedby another function 1224 and fed to a process function 1226 therebylimiting the total output to a useful output range.

Making reference now to FIG. 10, a pictorial representation of a flowchart for the proportional plus reset controller program is shown. Inthe preferred embodiment the Preset program is designed such that a callfrom the control program 1030 provides a list of variables necessary toevaluate the controller 1068 output. The structure of the subroutine isindicated by the Fortran statement given below.

SUBROUTINE PRESET (ERR, ERRX, G, TR, HL, XLL, RES, PRES)

The variables in the above equation are defined as follows:

                       English Language                                           FORTRAN Variables  Equivalents                                                ______________________________________                                        ERR                The current input                                          ERRX               The last input                                             G                  The controller                                                                proportional gain                                          TR                 The controller reset                                                          time                                                       HL                 The controller high                                                           limit                                                      XLL                The controller low                                                            limit                                                      RES                The controller integral                                                       output                                                     PRES               The controller total                                                          output.                                                    ______________________________________                                    

Again making reference to FIG. 10, where standard FORTRAN notation isused, the Preset subroutine 1068 first evaluates the integral part ofthe controller output according to equation: ##EQU1## The subroutine1068 next saves the current input ERR in storage location ERRX 1250 forthe following call to the subroutine 1068. The controller integraloutput RES 1252 is then checked against the high limit 1254 and the lowlimit 1256 to prevent reset/windup. The proportional part of the outputis computed and added to the integral part of the output integrator 1218to form the total output PRES 1258. PRES 1258 is checked against highlimit 1260 and low limit 1262 after which the proportional plus resetcontroller subroutine 1068 returns to the control task 1020.

As previously considered, the proportional plus reset controllersubroutine 1068 is used by the control task program 1020 during threedifferent phases of operation of the turbine system. During startup ofthe turbine system 10, the proportional plus reset controller subroutineprogram 1068 is used as a speed controller in order to regulate and holdthe speed of the turbine 10 at a predetermined value or at apredetermined acceleration rate. Because of the integral function of theproportional plus reset controller subroutine program 1068 the speed ofthe turbine system 10 can be held to within 1 rpm. Also, in order for anoperator to keep the speed of the turbine system 10 at a predeterminedvalue, an error offset input signal typical of a purely proportionalsystem is not required. Therefore, the reference and the controlledvariable, both turbine speed in this case, will be equal. Theproportional plus reset controller subroutine program 1068 is also usedin the megawatt controller feedback loop and the impulse chamberpressure controller feedback loop.

During turbine startup, the quantity REFDMD is the internal speedreference while WS is the actual turbine speed. GS1 and T1 are theproportional gain and reset time, HLS and 0. are the high and lowlimits. RESSPD is the integral part of the output, SPDSP is the totaloutput, and RESSPDX is the last value of the input.

In the megawatt controller during megawatt loop operation, REF1 is themegawatt set point, MW is the megawatt feedback, and GR2 is a ranginggain to convert from engineering units to per-unit form. GL2 and T2 arethe proportional gain and the reset time, while HEL and LEL are high andlow limits. RESMW is the integral output, Y is the total output, andRESMWX is the last input.

With impulse pressure loop operation, PISP is the set point for theimpulse pressure controller, PI is the feedback and GL3 and T3 are theproportional gain and the reset time. GR4 and 0. are the high and lowlimits, RESPI is the integral output, VSP is the total output, andRESPIX is the last input.

2. SPEED LOOP SUBROUTINE

Making reference not to FIG. 11, a speed loop program 1310 whichfunctionally is part of the arrangement shown in FIG. 5 is shown ingreater detail. The speed loop (SPDLOOP) program 1310 normally computesdata required in the functioning of the speed feedback loop in the loadcontrol comprising as shown in FIG. 5 the rated speed reference 1074,the actual turbine speed 1076, the compare function 1078, theproportional controller 1080 and the summing function 1072. During theload control, the speed feedback loop adjusts the load reference (andthus the governor valves) to correct for any turbine speed deviationfrom rated speed. The speed feedback loop uses a proportional controllerto accomplish this function. The speed loop subroutine 1310 is calledupon to perform speed control loop functions by the control program1020. In FIG. 11, the functioning of the proportional controller 1080 isshown in detail. The error output from the compare function 1078 is fedthrough a deadband function 1312. A proportionality constant (GR1) 1314and a high limit function (HLF) 1316 are included in the computation.

The speed loop (SPDLOOP) subroutine is called by the control task duringthe load control mode and when switching occurs between actual speedsignals. Subroutine form reduces the requirement for memory storagespace thereby reducing computer the expense required for operation ofthe DEH system 1100.

The deadband function 1312 provides for bypassing small noise variationsin the speed error generated by the compare function 1078 so as toprevent turbine speed changes which would otherwise occur. Systemswithout a deadband continuously respond to small variations which arerandom in nature resulting in undue stress in the turbine 10 andunnecessary, time and duty cycle consuming operation of the controlsystem. A continuous hunting about the rated speed due to the gain ofthe system would occur without the deadband 1312. The speed regulationgain GR1 at 1314 is set to yield rated megawatt output power speedcorrection for a predetermined turbine speed error. The high limitfunction HLS at 1316 provides for a maximum speed correction factor.

The turbine speed 1076 is derived from three transducers. The turbinedigital speed transducer arrangement is that disclosed in greaterelement and system implementation detail in the aforementioned ReutherApplication Ser. No. 412,513. Briefly, in the preferred embodiment fordetermining the speed of the turbine, the system comprises threeindependent speed signals. These speed signals consist of a veryaccurate digital signal generated by special electronic circuitry from amagnetic pickup, an accurate analog signal generated by a secondindependent magnetic pickup, and a supervisory analog instrument signalfrom a third independent pickup. The DEH system compares these signalsand through logical decisions selects the proper signal to use for speedcontrol or speed compensated load control. This selection processswitches the signal used by the DEH control system 1100 from the digitalchannel signal to the accurate analog channel signal or vice versa underthe predetermined dynamic conditions. In order to hold the governorvalves at a fixed position during this speed signal switching thecontrol program 1020 uses the speed loop subroutine 1310 and performs acomputation to maintain a bumpless speed signal transfer.

Making reference to FIG. 12, the speed loop (SPDLOOP) subroutine flowchart 1310 is shown in greater detail. Two FORTRAN statements signifythe operations of the speed loop subroutine program flow chart 1310.These statements are:

Call spdloop

    ref1 = refdmd + x

variables in the flow chart 1310 are defined as follows:

    FORTRAN VARIABLES                                                                              ENGLISH LANGUAGE EQUIVALENT                                  ______________________________________                                        REFMD            Load reference                                               WR               The turbine rated speed                                      REF1             Corrected load reference                                     WS               The actual turbine speed                                     TEMP             Temporary storage location                                                    variable                                                     SPDB             The speed deadband                                           GR1              The speed regulation gain                                                     (normally set to yield rated                                                   megawatt speed correction for                                                 a 180 rpm speed error)                                      X                Speed correction factor                                      HLF              The high limit function.                                     ______________________________________                                    

3. PLANT CONTACT CLOSURE INPUT (PLANTCCI) SUBROUTINE

A plant contact closure input subroutine 1150 as shown in FIG. 6 scansall the contact inputs tied to the computer through the plant wiring1126 and sets logic data images of these in designated areas within thememory 214 of the computer 210. Various situations call for the PLANTCCIsubroutine. The most common case represents a basic design feature ofthe DEH system; that is, the situation in which a change of state of anycontact input triggers a sequence of events interupt. A correspondinginterrupt program then calls the PLANTCCI subroutine to do a scan of allcontact inputs and to update the computer contact image table. Thus(under normal conditions) a contact scan is carried out only whennecessary. A block diagram illustrating the operation of the plantcontact closure input subroutine 1150 is shown in FIG. 13. The plantcontact closure input subroutine 1150 is also utilized when power to thecomputer 210 is turned on or when the computer buttons reset-run-resetare pressed on a maintenance panel 1410. Under these circumstances, aspecial monitor power-on routine 1412 is called upon. This programexecutes the computer STOP/INITIALIZE task 1414 described previously,which in turn calls the plant contact closure input subroutine 1150 forperformance of the initializing procedure.

The operator can also call the plant contact closure input subroutine1150 through the auxiliary synchronizer program 1114, if desired,whereby a periodic scan of the entire computer CCI system is implementedfor checking the state of any one or group of relays in the CCI system.This call is contingent upon the entry of a non-zero value for theconstant PERCCI from the DEH Operator's Panel keyboard.

4. AUXILIARY SYNCHRONIZER PROGRAM

With reference to FIG. 14, the block diagram shows an overall schemewhich illustrates the operation of the auxiliary synchronizer program1510. The auxiliary synchronizer program 1510 has two functions. Itperforms accurate counting to determine the time duration of importantevents to be described in more detail and it synchronizes the biddingfor execution of all periodic programs in the digital electrohydraulicsystem 1100 on a predetermined schedule. The AUX SYNC task is onpriority level E₁₆ (14₁₀) and is initiated by the 60 Hz synchronizingprogram of the Monitor every 1/10 sec. Highly accurate and stable timingis provided by a clock to align all parts of the system in a repetitiveworking pattern. Such timing sources are called clocks or synchronizers.Clocks may generate their timing pulses in a number of ways; the mostcommon clocks consist either of a very accurate electronic oscillator,or a timing circuit triggered by the 60 Hz supply frequency to thecomputer.

The DEH control system utilizes the line frequency as its timing source.As shown in FIG. 14, a clock pulse is generated every cycle (1/60 sec),and triggers a counting circuit in the computer Monitor system. TheMonitor is initialized to generate an interrupt every six cycles (1/10sec). When this interrupt occurs, the Monitor executes its own internalscheduling functions and then bids the AUX SYNC task to run. AUX SYNCproceeds to carry out its various timing calculations and bids allremaining periodic DEH programs.

OPERATOR'S PANEL AND FLASH PROGRAM

Referring now to FIGS. 15, 16 and 17, the control panel 1130 for thedigital electrohydraulic system 1100 is shown in detail. Specifiedfunctions have control panel buttons which flash in order to attract theattention of an operator. The FLASH task has two functions: it flashesappropriate lights to alert the operator to various important conditionsin the DEH system, and it sets contact outputs to pass these sameconditions to the Analog Backup and Boiler Control Systems. The FLASHtask is on priority level 5 and is bid by the AUX SYNC task every 1/2sec. The concept behind the FLASH task is that flashing will attract theoperator's attention much more quickly than simply maintaining a steadyon condition. Most of the flashing lights indicate contingencyconditions; a few indicate such things as invalid keyboard entries orthat the DEH system is ready to go on automatic control. The flashingfrequency is set at 1/2 sec on and 1/2 sec off as long as the conditionexists. At the termination of the flashing condition, the correspondinglights and contacts are turned off.

A total of nine conditions are continually monitored for flashing by theFLASH task. These are listed below with a brief description of each.

    __________________________________________________________________________    1.                                                                              Reference Low Limit                                                                          --                                                                              The turbine load reference is                                                 being limited by the low load                                                 limit.                                                     2.                                                                              Reference High Limit                                                                         --                                                                              The turbine load reference is                                                 being limited by the high load                                                limit.                                                     3.                                                                              Valve Position Limit                                                                         --                                                                              The turbine governor valve output                                             is being limited by the valve                                                 position limit.                                            4.                                                                              Throttle Pressure Limit                                                                      --                                                                              The turbine load reference is                                                 being run back because throttle                                               pressure is below set point. No                                               light is flashed in this case but                                             a contact output is set during                                                the throttle pressure limiting.                            5.                                                                              DEH Ready for Automatic                                                                      --                                                                              The DEH control system has tracked                                            the manual backup system and is                                               ready to go on automatic control.                          6.                                                                              Valve Status Contingency                                                                     --                                                                              While on automatic control, the                                               DEH system has detected a valve                                               LVDT position not in agreement                                                with its corresponding analog                                                 output.                                                    7.                                                                              Governor Valve Contingency                                                                   --                                                                              A governor valve LVDT position is                                             not in agreement with its analog                                              output.                                                    8.                                                                              Throttle Valve Contingency                                                                   --                                                                              A throttle valve LVDT position                                                is not in agreement with its                                                  analog output.                                             9.                                                                              Invalid Request                                                                              --                                                                              An invalid keyboard entry has                                                 been made.                                                 __________________________________________________________________________

In order to determine whether to flash a light or to suppress flashing,the FLASH task maintains two arrays in core memory. One of these iscalled LIMIT and contains the current value of the nine limiting orflashing conditions listed above, as they are set by various other DEHprograms. The second array is called OLDLIMIT and is an image of theimmediate past value of the LIMIT array. These two arrays are examinedevery 1/2 sec by the FLASH task according to the following table ofcombinations:

    FLASH TASK LAMP COMBINATIONS                                                  LIMIT        OLDLIMIT      Action                                             ______________________________________                                        0            0             Do Nothing                                         0            1             Turn Light Off                                     1            0             Turn Light On                                      1            1             Turn Light Off                                     ______________________________________                                    

After the proper action is taken by the FLASH task, the OLDLIMIT arrayis then updated to agree with the current LIMIT array for the next passthrough the task 1/2 sec later.

A third array called CCOFLAG is also maintained by the FLASH task inorder to set contact outputs when a limiting condition exists. Thecontact outputs are not set and reset regularly (as are the flashinglights) but rather the contacts are set and remain on as long as theflashing condition exists. When the flashing condition ceases thecontacts are reset. A table of combinations illustrating this action

    FLASH TASK CONTACT COMBINATIONS                                               LIMIT        CCOFLAG       Action                                             ______________________________________                                        0            0             Do Nothing                                         0            1             Reset Contact                                      1            0             Set Contact                                        1            1             Do Nothing                                         ______________________________________                                    

It should be noted that only the first five flash conditions listedabove have contact outputs associated with them; the remaining foursimply flash Operator's Panel lights.

The control of the operation of the DEH control system 1100 is greatlyfacilitated for the operator. by the novel layout of the operator'spanel 1130, the flashing and warning capabilities thereof, and theinterface provided with the turbine control and monitor functionsthrough the pushbutton switches. In addition, simulated turbineoperation is provided by the DEH system for operator training or otherpurposes through the operation of the appropriate panel switches duringturbine down time. Further, it is noteworthy that manual and automaticoperator controls are at the same panel location for good operatorinterface under all operating conditions. More detail on the functioningof the panel pushbuttons is presented in Appendix 2 and elsewhere in thedescription of the DEH programs herein.

In addition the layout of the panel 1130 of FIGS. 15, 16 and 17 isunique and very efficient from operation and operator interfaceconsiderations. The control of the DEH system 1100 by the buttons of thepanel 1130 and the software programs thereto provides improved operationof the computer 210 and turbine generator 10.

Software details of the panel 1130 interface are available in theappendices 3,4,5 and 6.

In the field-installation phase of computer control systems, checkout ofall parts of the system can be a tedious and frustrating chore.Debugging of programs, computer hardware and plant wiring is often aslow and painful process, and isolation of problems to one of theseareas is sometimes difficult. It is during this time that the CCO TESTtask provides a powerful tool for helping to bring the DEH system tofull operating capabilities quickly.

The CCO TEST task is patterned along the lines of the DEH Input/Output(I/O) listing. The I/O list has a description of all contact outputs innumerically increasing order, from C001 to C224. The list includes averbal description of the contact output function, its bit position,hardware word, set channel, and cabinet-half-shell terminal connectioninformation. Since each contact output is identified by its C-number, toset or reset a contact or group of consecutive contacts, it is necessaryonly to type in the contact number(s) from the Programmer's Console andbid the CCO TEST task. Since analog outputs are essentially groups ofcontact outputs, the CCO TEST task may also be used to set any value onan analog output. This allows additional soft-ware and hardware testingprior to interfacing of the entire system.

5. SEQUENCE OF EVENTS INTERRUPT PROGRAM

Once the PLANTCCI subroutine identifies the plant condition that changedstate and activated the sequence of events program 1124 the execution ofan appropriate function program may be initiated in accordance with thetask priorities. Contact inputs scanned by the CCI subroutine are setforth in the input/output signal list in Appendix 4.

6. BREAKER OPEN INTERRUPT PROGRAM

Referring now to FIG. 1, if the breaker 17 opens thereby removingelectrical load 19 from the generator 16, the turbine system 10 willbegin to accelerate. The acceleration will overspeed the turbinegenerator system 10 and damage the turbine generator system 10 if it isnot checked. It is mandatory that the turbine governor valves be closedan instant after the breaker opens, to cut off steam flow. The controlsystem then reverts to speed control and positions the governor valvesto maintain synchronous speed. In order to restrict turbine overspeedwhen the breaker 17 opens, the breaker open contact is used to producean interrupt. The Monitor interrupt handler then runs a BREAKER OPENINTERRUPT program 1710 which immediately closes the governor valves bysetting the appropriate analog output to zero. An independent hydraulicoverspeed protection system shown in Ser. No. 189,322 by Fiegbein andCsanady also acts directly under predetermined conditions to close thegovernor valves GV1-GV8 and the throttle valves TV1-TV4 by dumping thehydraulic fluid in the valve actuators thereby giving additionalprotection to the turbine system 10. When the hydraulic overspeedprotection system reacts to a breaker open operation (i.e. a full loadrejection), the turbine steam valves are directly and immediately closedand the DEH system functions on a following basis to update its valveposition outputs to call for valve closure. When a partial loadrejection occurs, i.e. the breaker remains closed, a control strategylike that described in the aforementioned Birnbaum Braytenbah andRichardson Patent 3,552,872 is effected by the DEH system.

7. TASK ERROR PROGRAM

A task error program 1810 shown in FIG. 6 has supervisory control overall the other programs in the DEH system 1100. If any program is notfunctioning properly in correspondence to certain predefined errorconditions, the task error program 1810 will switch the DEH system 1100to manual control thereby preventing any accident, overload, underload,overspeed, or underspeed from happening. Thus, the TASK ERROR program1810 switches control of the turbine from automatic to manual if certainimportant control tasks are disabled by the Monitor during input/outputactivity. The TASK ERROR program 1810 is initialized by the Monitorerror handler.

The P2000 Monitor is composed of a variety of programs which handle allI/O activity for the DEH system. Thus, when some turbine control programwishes to use the I/O system, it calls the proper Monitor handler with aset of arguments describing the function to be performed. The handlerthen carries out the request and returns to the calling task at thecompletion of the function. However, in usual applications, if thehandler finds erroneous information in the arguments passed along by thecalling task, then the I/O request is ignored and the calling task isdisabled. An example of such an error is a zero, negative ornon-existent register number when calling the contact output handler. Anexample of the usual operation of the P2000 Monitor in this particularcase, i.e. in the DEH system, would be when a turbine operating programsuch as the panel task 1112 calls to use an input/output system such asthe panel lamp program 1132. The panel task 1112 calls the monitorprogram 1122 with a set of arguments describing the function to beperformed. The monitor program 1122 then carries out the request andreturns to the panel task program 1112 at the completion of thefunction. However, if the monitor program 1122 finds erroneousinformation in the arguments or data passed along by the panel task 1112then the input/output request for the panel lamp 1132 is ignored and thepanel task 1112 is disabled. A monitor reference manual, TP043, of theComputer and Instrumentation Division of the Westinghouse ElectricCorporation describes in detail all possible error conditions.

TURBINE TRIP INTERRUPT program provides for throttle and governor valveclosure immediately after the turbine latch mechanism is released. TheTURBINE TRIP INTERRUPT program is initiated by the Monitor interrupthandler.

The mechanical latching mechanism of a turbine has a series ofinterlocks which are designed to trip the turbine off the line when anyserious discrepancy is found in the system. Such factors as hydraulicfluid system, mechanical levers, emergency trip button, and solenoidsoperated by detection circuits may unlatch the turbine. When thishappens, all throttle and governor valves must be closed to cut offsteam flow immediately, after which the turbine begins to decelerate.

8. TURBINE TRIP INTERRUPT PROGRAM

In FIG. 6, a turbine trip interrupt program 1850 is shown coupled to theplant wiring 1126 and to the throttle valves TV1-TV4 and the governorvalves GV1-GV8 1021. If the turbine system 10 reaches a trip condition,and reaches a predetermined speed for example 105% of synchronous speed,a latch open contact 1852 changes state and indicates a trip to theturbine trip interrupt program 1850 by means of an interrupt signal. TheMonitor interrupt handler then runs the TURBINE TRIP INTERRUPT program,which immediately calls for throttle and governor valve closure.Simultaneously the analog backup system detects the trip condition andprovides a large closing bias voltage to the throttle and governor valveservo system, thus assuring via redundant circuits that all valves areclosed. By closing all the valves in the turbine system 10, dangerousturbine overspeed and other conditions are avoided.

9. PANEL INTERRUPT PROGRAM

The PANEL INTERRUPT program responds to Operator's Panel pushbuttonrequests by decoding the pushbutton identification and bidding the PANELtask to carry out the appropriate response. The PANEL INTERRUPT programis initiated by the Monitor interrupt handler.

The DEH turbine control system is designed to provide maximumflexibility to plant personnel in performing their function of operatingthe turbine. This flexibility is evidenced by an Operator's Panel withan array of pushbuttons arranged in functional groups, and an internalsoftware organization which responds immediately to pushbutton requestsby the operator. The heart of this instant response is the interruptcapability of the DEH control system.

Pressing any panel pushbutton activates a diode-decoding network whichidentifies the pushbutton, sets a group of six contacts to anappropriate coded pattern, and generates an interrupt to the computer.The Monitor interrupt handler responds within microseconds and runs thePANEL INTERRUPT program, which does a demand contact input scan of thespecial panel pushbutton contacts and bids the PANEL task to carry outthe function requested by the operator.

10. VALVE TEST, VALVE POSITION LIMIT AND VALVE INTERRUPT PROGRAM

Certain valve testing and limiting functions have been a traditionalturbine control feature over the years to provide assurance of theemergency performance of valves and to give the operator a finaloverride on the control valve position. Thus, on line testing ofthrottle valves periodically will detect potential malfunctions of thethrottle valve mechanism which could be dangerous if not corrected. Inaddition, valve position limiting of the governor valves during on lineoperation provides a manual means of limiting steam flow from theOperator's Panel.

In the DEH control system these two important functions are initiated byappropriate pushbuttons on the panel. As long as the operator pressesone of these pushbuttons, the proper action is carried out by theCONTROL program. When the operator releases any of these pushbuttons,this generates a special interrupt to terminate the action which hasbeen performed.

Referring again to FIG. 6, a valve test program 1810 and a valveposition limit program 1812 are subroutines of the control task program1020. The valve test program 1810 tests the operation of anypredetermined valve or valves such as the throttle valves TV1 throughTV4 by the operator pressing a valve test button 1814 of FIG. 16 on theoperator's panel 1130. The valve position limit program 1812 of thecontrol task 1020 operates when an operator presses either of the twobuttons, valve position limit lower 1816 or valve position limit raise1818 of FIG. 16.

Referring again to FIG. 16, upon the release of the valve test button1814, the valve position limit lower button 1816 or the valve positionlimit raise button 1818 by an operator, the valve interrupt program 1158shown in FIG. 6, is run by the monitor program 1122. The monitor program1122 runs the valve interrupt program 1158 and thereby resets variousflags and counters thus signaling to the control task 1020 that theaction is to cease.

11. STOP/INITIALIZER PROGRAM

The STOP/INITIALIZE task 1162 (FIG. 6) initializes the DEH system to aknown starting condition after the computer has stopped for any reason.(Note that stop here includes placing the computer out of sync.) TheSTOP/INITIALIZE task is assigned the highest priority level F₁₆ (15₁₀)and is bid by special insert instructions in the Monitor POWER-ONroutine.

To control a continuously operating process successfully, a computermust be designed to run for very long periods of time without stopping.However, it must be recognized that power failures, computer hardwaremalfunctions of program errors will eventually cause all controlcomputers to stop at some time in their operation. At these times,backup systems take over the process while the necessary maintenance isdone on the computer or its software.

In FIG. 6, a stop/initializer program 1162 is shown ancillary to theclock program 1120. Should the DEH system 1100 have a power failure orbe turned off, the stop/initializer program 1162, which has the highestpriority (FIG. 9) of any program in the DEH system 1100, starts to run.Within the time that the voltages of the power supplies, not shown,decay to an unusable limit, the stop/initializer program 1162 sets theDEH system 1100 into a known state for the impending stop. Uponrestarting, the stop/initializer program 1162 resets the system to theknown state, i.e. it sets all contact and analog outputs to the throttlevalves TV1 through TV4 and the governor valves GV1 through GV8 shown inbox 1021 at reset position; all internal counters and logic states arereset; certain systems counters are set to starting values; a scan ofall contact inputs from the plant wiring 1126 is carried out and thelogic program 1110 is executed to align the DEH system 1100 to existingplant conditions. Finally, the controller reset lamp 1820 on theoperator's panel 1130 as shown in FIG. 16 is turned on and the DEHsystem 1100 is ready to restart.

When the operator presses the CONTROLLER RESET button, thusacknowledging the fact that the DEH system is operational again, allperiodic programs begin to execute regularly and the control systemtracks to the existing plant conditions. Operation from this point on isidentical in all respects to normal execution of the DEH control systemprograms.

12. VISUAL DISPLAY PROGRAM

Visual display of numerical information which resides in memory has beena traditional function of control computer systems. This featureprovides communication between the operator and the controller, withboth display and changing of internal information usually available.Continuous display of a quantity provides visual indication of trends,patterns and dynamic response of control system variables; periodicallyupdated values of the displayed quantity are entered into the windows sothat fast changes may readily be observed by operating and technicalpersonnel.

The DEH control system has provision for visual display of six importantcontrol quantities through dedicated individual pushbuttons. Inaddition, complete valve status (i.e. position) may be displayed througha group of appropriate pushbuttons; all remaining control systemvariables, parameters or constants may be displayed through anotherpushbutton, in conjunction with keyboard-entered dictionary addresseswhich select the desired quantity for display.

The visual display program 1134 as shown in FIG. 6 is connected with thepanel interrupt program 1156 and the auxiliary synchronizer program1114. The visual display program 1134 controls the display windows 1138with a reference window 1852 and a demand window 1854. The demand window1854 and the reference window 1852 are also shown in FIG. 16 as part ofthe operator's panel 1130. By pressing an appropriate button such as thereference button 1856 a reference value will be displayed in thereference window 1852 and a demand value will be displayed in the demandwindow 1854. Similarly, for example, if a valve position limit displaybutton 1858 is pressed a valve position limit value will be displayed inthe reference window 1852 and the corresponding valve variable beinglimited is displayed in the demand window 1854. Upon pressing the loadrate button 1858 the load rate will be displayed in the reference window1852. In addition, a keyboard 1860 has the capability through anappropriate program to select virtually any parameter or constant in theDEH system 1100 and display that parameter in the reference window 1852and the demand window 1854.

13. ANALOG SCAN PROGRAM

In order to carry out its function, a computer control system must beprovided with input signals from the process or plant variables whichare to be controlled. However, the vast majority of real processvariables (for example pressure, temperature and position) are analog orcontinuous in their natural form, whereas the organization and internalstructure of computers is digital or discontinuous in nature. This basicdifference in information format between the controller and thecontrolled process must be overcome with interfacing equipment whichconverts process signals to an appropriate computer numerical value.

A device which can accomplish this function is the analog-to-digital(A/D) converter. The A/D converter provides the interface between plantanalog instrumentation and the digital control system. Normally theanalog signal as picked up from a transducer is in the millivolt or voltrange, and the A/D converter produces an output bit pattern which may bestored in computer memory. A/D converters can only convert a limitednumber of analog inputs to digital form in a given interval of time. Theusual method of stating this limit is to indicate the number of points(analog inputs) which can be converted in 1 sec. Thus, the A/D converterused in the DEH system has a capacity of 40 pps. Since the total numberof analog inputs to the DEH system may be as high as 224, depending onthe type of turbine to be controlled and the control system optionsselected, most of these must be scanned at a reduced frequency.

The nature of the plant variables which represent the analog inputs, andthe sampling frequency of control programs using these inputs, arenormally considered when one determines the scanning frequency ofvarious analog input signals. In the DEH system, the control programsexecute once a second and the primary analog signals used by the controlsystem are generated megawatts, impulse pressure, throttle pressure,turbine speed and valve position. Since each of these variables maychange a significant amount in a few seconds, all of these are scannedonce a second. On the other hand, the majority of the analog inputs tothe ATS program are temperatures which require minutes beforesignificant changes in them may be observed. Consequently, alltemperatures in the DEH system are scanned once a minute. The ATSprogram also requires a group of vibrations, which are scanned onceevery 5 sec, and a group of miscellaneous variables which are scannedonce every 10 sec.

A timing diagram, or scan-frequency chart, is shown in FIG. 19 toindicate the complete analog scanning system for an end-bar-lift turbinehaving two throttle valves and two governor valves. The scanning patternhas been designed so that the A/D converter and the DEH computer systemhave an approximately uniform distribution of activity. A close look atFIG. 19 will indicate that once every 15 sec the analog scan systemperforms what is known as a SPAN/ADJUST operation. The purpose of thisis to adjust the analog input bit patterns to account for drift in theA/D converter electronic circuitry and to account for the frequencyvariations, since the A/D converter operates on a voltage to frequencyconversion principle.

The analog scan program 1116, shown in FIG. 6 periodically scans allanalog inputs to the DEH system 1100 for control and monitoringpurposes. The function of the analog scan program 1116 is performed intwo parts. The first part of the analog scan program 1116 comprises thescanning of a first group of analog inputs. Values of scanned inputs areconverted to engineering units and the values are checked againstpredetermined limits as required for computations in the DEH computer.

The second part of the function of the analog scan program 1116comprises the scanning of the analog inputs required for the automaticturbine startup program as shown in FIG. 6. Conversion andlimit-checking of this latter group of inputs is performed by anotherprogram. The automatic turbine startup program is shown in FIG. 6 as theATS periodic program 1140, the ATS analog conversion routine 1142 andthe ATS message writer program 1144.

A functional organization diagram of the ANALOG SCAN task is shown inFIG. 18. The AUX SYNC task bids the ANALOG SCAN program every 1/2 sec.The ANALOG SCAN task then selects the appropriate group of inputs to bescanned, according to the timing diagram of FIG. 19, and calls theanalog input handler portion of the Monitor. This handler triggers theA/D converter hardware to scan these points and suspends the ANALOG SCANtask until the bid patterns are available. The handler then restarts theANALOG SCAN task, which converts the input bit patterns to engineeringunits, does appropriate limit-checking and makes logical decisions, andthen exists until the next call from the AUX SYNC task, 1/2 sec later.

14. LOGIC TASK

The LOGIC task determines the operational status of the DEH turbinecontrol system from information provided by the plant, the operator, andother DEH programs.

Referring now to FIG. 20, a block diagram representing the operation ofthe logic task 1110 is shown. A contact input from the plant wiring 1126triggers the sequence of events or interrupt program 1124 which callsupon the plant contact closure input subroutine 1150 which in turnrequests that the logic program 1110 be executed by the setting of aflag called RUNLOGIC 1151 in the logic program 1110. The logic program1110 is also run by the panel interrupt program 1156 which calls uponthe panel task program 1112 to run the logic program 1110 in response topanel button operations. The control task program 1020 in performing itsvarious computations and decisions will sometimes request the logicprogram 1110 to run in order to update conditions in the control system.In FIG. 21, the functioning of the logic program 1110 is shown. FIG. 22shows a more explicit block diagram of the logic program 1110.

The mechanism for actual execution of the LOGIC program is provided bythe AUX SYNC task, which runs every 1/10 sec and carries out thescheduled and demand bidding of various tasks in the DEH system. AUXSYNC checks the state of the RUNLOGIC flag and, if it is set, bids theLOGIC task immediately. Thus, the maximum response time for LOGICrequests is 1/10 sec; on the average the response will be much fasterthan this.

In order to allow immediate rerunning of the LOGIC task should systemconditions require, the LOGIC program first resets RUNLOGIC. Thus anyother program may then set RUNLOGIC and request a bid which will becarried out by the AUX SYNC program within 1/10 sec. There are two majorresults of the LOGIC task: the computation of all logic states necessaryfor proper operation of the DEH system, and the processing of all statusand monitor lamp contact outputs to inform the plant control system andoperating personnel of the state of the DEH system.

The logic program 1110 controls a series of tests which determine thereadiness and operability of the DEH system 1100. One of these tests isthat for the overspeed protection controller which is part of the analogbackup portion of the hardwired system 1016 shown in FIG. 4. Generally,the logic program 1110 is structured from a plurality of subroutineswhich provide the varying logic functions for other programs in the DEHprogram system, and the various logic subroutines are all sequentiallyexecuted each time the logic program is run.

LOGIC CONTACT CLOSURE OUTPUT SUBROUTINE

The logic task 1110 includes a subroutine called a logic contact closureoutput subroutine 1910 (FIG. 20) therein. The logic contact closureoutput subroutine 1910 updates all the digital outputs to the statuslamps and contacts 1128 for transmission thereto. The logic program 1110handles a great number of contact outputs thereby keeping the outputlogic states of the DEH computer current. In addition, certain logicalvariables, which are normally set by the PANEL task, must be aligned bythe LOGIC task with conditions as they exist instant by instant in thepower plant. To do these functions in-line for each contact output inthe LOGIC task would take considerable core storage to accommodate theindividual situations. Thus, the logic contact closure output subroutine1910 reduces the total storage requirements otherwise required for thelogic program 1110.

MAINTENANCE TEST

In order to take advantage of the full flexibility, adjustability anddynamic response of the DEH system 1100 a maintenance test system 1810is provided. The maintenance test program 1810 allows an operator tochange, adjust or tune a large number of operational parameters andconstants of the DEH system 1100. The constants of the DEH system 1100can therefore be modified without extensive adjustment or reprogramming.An operator is able to optimize the DEH system 1100 from the controlpanel 1130 as shown in FIGS. 15 and 16 which allows for an essentiallyinfinite variability in the choice of constants. Great flexibility andcontrol is therefore available to an operator.

In addition, the maintenance test program 1810 allows an operator to usea simulation mode for operator training purposes.

TURBINE SUPERVISION OFF LOGIC

In the DEH control system, the ATS program 1141 is an optional featurewhich automatically accelerates the turbine during speed control andperforms monitoring functions during load control. When this option ispurchased by the user, the operator's panel has an extra back-lightedpushbutton which allows these turbine supervisory functions to be turnedon or off at the operator's discretion. In addition to this off-oncontrol, another mechanism exists to turn off the supervision programs.To understand this method, it is first necessary to realize thatsupervision means monitoring of a large number of analog inputs whichrepresent various turbine metal and steam temperatures, steam pressures,and turbine mechanical vibrations. These analog inputs are converted todigital signals by an electronic analog-to-digital (A/D) converter andan analog scan program. As happens with any device occasionally, the A/Dconverter may be out of service for a short interval of time; since allanalog inputs are then meaningless, it is necessary to immediately turnthe turbine supervision programs off.

When the supervisory programs are off, whether due to the operatorpressing the pushbutton or due to the A/D converter being out ofservice, the lamp behind the pushbutton is turned on. To place thesupervisory programs back on, it is only necessary to press the buttonagain and, assuming the A/D converter is in service, the lamp will beturned off.

COMPUTER SET MANUAL LOGIC

When the DEH system is in automatic control, it is possible for certainconditions to occur which require transfer to manual operator control.One of these is the case in which the maintenance test switch is movedto the test position. Even though a wired connection places the controlin manual operation, the DEH LOGIC program sets a contact outputrequesting transfer to manual as a backup. The second situation occurswhen the turbine is on automatic speed control and all speed inputsignals fail, as determined by the speed selection program in theCONTROL task. This speed channel failure will also require transfer tomanual operation by a contact output from this LOGIC task.

BREAKER LOGIC

The state of the main circuit breaker which connects the generator tothe power system determines a primary control strategy of the DEHsystem. When the breaker is open, the DEH system is on speed control andthus positions the throttle and governor valves to maintain speed demandas requested by the operator, an automatic startup program, or anautomatic synchronizer. When the breaker is closed, the DEH system is onload control and thus positions the governor valves to maintain loaddemand as requested by the operator or by an automatic dispatchingsystem.

The function of the breaker logic program is to detect changes in thestate of the main breaker and take the appropriate action. When thebreaker opens, it is necessary to reset the breaker flip-flop to placethe DEH control system on speed control; in addition, both the REFERENCEand DEMAND are set to synchronous speed, and the speed integralcontroller is reset to zero. The control system will then position thegovernor valves to maintain synchronous speed. When the breaker closesand the unit is synchronized to the line, the breaker logic program mustset the breaker flip-flop to place the DEH system on load control; inaddition both the REFERENCE and DEMAND are set to pick up an initialmegawatt load so that the turbine does not tend to motor. The controlsystem will then position the governor valves to maintain this initialload.

Referring again to FIG. 1, upon synchronization of the turbine system 10with a power grid, not shown, the governor valves GV1 through GV8 mustallow sufficient steam to flow through the turbine system 10 to overcometurbine system losses. Otherwise, upon synchronization of the generator16 with other generators in the power grid by closing the breakers 17,the turbine system 10 would as already indicated have a tendency tomotor. The DEH control system 1100, in order to prevent motoring andsubsequent damage to the low pressure turbine section 24, automaticallyopens the governor valves GV1 through GV8 such that a predetermined loadis picked up by the generator 16 upon synchronization.

The value of the initial megawatt pickup is defined as MWINIT uponsynchronization is entered from the keyboard 1860 in FIG. 16 and istypically set at about 5% of the rating of the turbine-generator 10. Inthe load control system 1814, as shown in FIG. 23, the actual megawattpickup is modified by a factor which is the ratio of the rated throttlepressure to the existing throttle pressure at synchronization. Thisfactor is utilized by the DEH system 1100 in maintaining approximatelythe same initial megawatt load pickup whether the turbine system 10 issynchronized at rated throttle pressure or at some lower or even higherthrottle pressure.

A second condition must be handled by the breaker logic program toproperly position the governor valves in picking up initial load. Thisconcerns the fact that the governor valves just prior to synchronizingwill be at some small position necessary to maintain synchronous speed.Then immediately after synchronization the initial megawatt pickup mustbe added to the existing valve position. Since the existing position iscomputed by the speed control program and the new position will becomputed by the load control program, then an equivalent load positionmust be computed from the existing speed position. Reference is made toAppendix 3 for details on the Breaker Logic Program.

MEGAWATT FEEDBACK LOGIC

Megawatt feedback is one of the two major loops used on turbine loadcontrol to maintain the governor valves at the correct position. Theother feedback is impulse pressure; between these two loops it ispossible to adapt the computer outputs to account for valvenon-linearities and to assure that the megawatt setting in the referencewindow is actually being supplied by the turbine/generator.

The megawatt feedback logic places the megawatt loop in service onrequest from an operator's panel pushbutton, providing all permissiveconditions are satisfied, and removes the loop from service from theoperator's panel pushbutton or when any condition exists which requiresremoving the megawatt feedback. Placing the loop in service or removingit is done bumplessly, so that the governor valves remain at the sameposition. In addition, the REFERENCE and DEMAND values are automaticallyadjusted to agree with the new state of the DEH control system.

Referring to FIG. 25, a block diagram of the megawatt feedback loop isshown in greater detail than in FIG. 5. It should be noted that thespeed compensated reference 1087, at the input of multiplicationfunction 1086, is multiplied by the megawatt compensation 1089. Themultiplication of the signals instead of a differencing provides anadditional safety feature since the loss of either of the signals 1087or 1089 will produce a zero output rather than a runaway condition.

IMPULSE PRESSURE FEEDBACK LOGIC

Impulse pressure feedback is the other of the two major loops used inthe turbine load control to maintain the governor valves at the correctposition. The impulse pressure feedback logic places the impulsepressure feedback loop in service on request from an operator's panelpushbutton, providing all permissive conditions are satisfied, andremoves the loop from service on request from the operator or when anycondition exists which requires removing impulse pressure feedback.Placing the loop in service or removing it is done automatically andbumplessly, so that the governor valves remain at the same position.With a digital computer, bumpless transfer is achieved without the useof elaborate external circuitry because of the digital computationalnature of the machine. A value can be computed instantaneously andinserted in the integrator 1218 of the proportional plus resetcontroller subroutine 1068 as shown in FIG. 9. In the preferredembodiment of the Digital Electro-Hydraulic control system 1100, theproportional plus reset controller 1168 is utilized by the followingfunctions: the megawatt feedback loop 1091, the impulse pressurefeedback loop 1816 and the speed feedback loop made up of the ratedspeed reference 1074, the compare function 1076 and the actual turbinespeed function 1076.

During the process of accelerating a turbine on automatic speed control,the normal steps of operation may be summarized as follows: latch androll the turbine on throttle control, accelerate to near synchronousspeed, transfer to governor valve control, accelerate to synchronousspeed, and synchronize the turbine with the power system. Most turbinesare brought on the line with conventional automatic synchronizingequipment which carefully matches turbine conditions with power systemconditions before automatically closing the main generator breaker.

The DEH control system 1100 provides an interface with synchronizingequipment by turning over supervision of the turbine reference anddemand to the automatic synchronizer, which provides raise and lowerpulses to the DEH system via contact inputs. Each pulse will raise andlower the turbine speed reference one rpm, thus providing the mechanismfor adjusting the turbine speed to the power system. Provision has beenmade in the DEH system to allow selection of the auto sync mode througha pushbutton on the operator's panel or from an automatic turbinestartup program, while the auto sync mode may be rejected by simplypressing the OPER AUTO pushbutton on the panel. The automaticsynchronizer (auto sync) logic program detects those conditionsconcerned with auto sync, and sets all logical conditions accordingly,The turbine 10 operates in accordance with actions generated by the DEHcontrol program in response to the synchronizer signals. FIG. 27 shows aflow chart of the automatic synchronizer logic program.

Because of the extreme accuracy of the ATS program 1141 in controllingthe speed of the turbine 10 synchronization can be and preferably isperformed without external automatic synchronizer equipment.

AUTOMATIC DISPATCH LOGIC

During the process of operating a turbine on automatic load control, thenormal method of changing load is by entering new values of load demandfrom the keyboard, as described in the operating instructions. Then byusing the GO and HOLD pushbuttons in conjunction with the load ratepushbutton, the operator may supervise the loading on the turbine whichis actually carried out by the DEH system of control programs. This willresult in the desired load being supplied to the power system by theturbine/generator.

Another method of supervising load on the turbine is through use of aremote automatic dispatching system. By turning over supervision of theturbine reference to an ADS operating mode, which provides raise andlower pulses whose width determines the requested load change, the DEHcontrol system allows the turbine loading to be coordinated by a centraldispatching office which can allocate total utility load on an economicbasis to all units in the power system. Provision has been made in theDEH system to allow selection of the automatic dispatch mode through apushbutton 1870 (FIG. 16) on the operator's panel; in addition, the ADSmode may be rejected by simply pressing the operator automaticpushbutton on the panel. The automatic dispatch logic program detectsthose conditions concerned with ADS, and sets all DEH statesaccordingly. A flow chart for the automatic dispatch logic program isshown in FIG. 28. It is triggered into operation on demand for automaticdispatch on order to interface the remote data with the DEH system.

AUTOMATIC TURBINE STARTUP (ATS) LOGIC

Modern methods of starting up turbines and accelerating to synchronousspeed require careful monitoring of all turbine metal temperatures andvibrations to assure that safe conditions exist for continuedacceleration. Until recently, these conditions have been observed byplant operators visually on various panel instruments. However, all ofthe important variables are rarely available from the plantinstrumentation, and even if they were, the operator can not always bedepended upon to make the right decision at a critical time. In additionto these factors, it is impossible to instrument the internal rotormetal temperatures, which are extremely important for indicatingpotentially excessive mechanical stresses.

To improve the performance at startup, automatic turbine acceleratingprograms have been written and placed under computer control. Suchprograms monitor large numbers of analog input signals representing allconceivable turbine variables, and from this information the programmakes decisions on how and when to accelerate the unit. In addition,these programs numerically solve the complex heat distribution equationswhich describe temperature variations in the critical rotor metal parts.From these thermal computations it is possible to predict mechanicalstresses and strains, and then to automatically take the proper actionin the acceleration of the turbine.

The DEH system has such an automatic turbine startup program availableas an optional item. Besides supervising the acceleration as describedabove, the program provides various messages printed on a typewriter tokeep the operator informed as to the turbine acceleration progress. Inaddition, a group of monitor lamps are operated to indicate key pointsin the startup stages and to indicate alarm or contingency conditions.The automatic turbine startup logic program detects those conditionsconcerned with this DEH feature and sets all logical states accordingly.

REMOTE TRANSFER LOGIC

In the DEH turbine control system philosophy, the operator has overallautority in a control system hierarchy which has three general states:manual operation, operator automatic control, and remote automaticcontrol. The manual operating mode is a contingency state which is usedonly when the computer is not available, as when the software controlsystem is being tuned or modified. The operator automatic mode is thenormal operating state during which speed/load demand and all otheroperating data are entered and displayed from the keyboard by theoperator. Remote automatic control modes are those in which speed/loaddemand and rate are supervised from a source outside the basic DEHsystem.

The DEH Operator's Panel is the focal point of turbine operation; it hasbeen designed to make use of the latest digital techniques to providemaximum operational capability. The Operator's Panel provides theprimary method of communicating information and control action betweenthe operator and the DEH Control System. This is accomplished through agroup of pushbuttons and a keyboard (which together initiate a number ofdiverse actions), and two digital displays (which provide the operatorwith visual indication of internal DEH system numerical values).

When pressed, any of the buttons on the Operator's Panel providemomentary action during which a normally-open contact is connected to anelectronic diode matrix. Operation of a button energizes a commoncomputer interrupt for the Operator's Panel and applies voltage to aunique combination of 6 contact inputs assigned as a pushbutton decoder.The diode matrix may be used to identify up to 60 pushbuttons. When abutton is pressed, the associated interrupt is read within 64 μ sec, andthe corresponding contact inputs scanned and stored in computer memoryas a bit pattern for further processing.

Each of the buttons on the panel are backlighted. When a button ispressed and appropriate logical conditions exist, the lamp is turned onto acknowledge to the operator that the action he initiated has beencarried out. Should the proper logical conditions not be set, the lampis not turned on. This informs the operator that the action he requestedcannot be carried out.

A few of the buttons are of the digital push-push type which when pushedonce initiate an action, and when pushed again suppress that action.Some of these buttons also contain a split lens which indicates oneaction in the upper half of the lamp and another (usually opposite)action in the lower lens. In addition, certain button backlights areflashed under particular operating circumstances and conditions.

The buttons and keys on the Operator's Panel may be grouped in broadfunctional groups according to the type of action associated with eachset of buttons. A brief description of these groups follows:

1. CONTROL SYSTEM SWITCHING - These buttons alter the configuration ofthe DEH Control System by switching in or out certain control functions.Examples are throttle pressure control and impulse pressure control.

2. DISPLAY/CHANGE DEH SYSTEM PARAMETERS - These buttons allow theoperator to visually display and change important parameters whichaffect the operation of the DEH system. Examples are the speed and loaddemand, high and low load limits, speed and and rate settings, andcontrol system tuning parameters.

3. OPERATING MODE SELECTION - This group of buttons provides theoperator with the ability to select the turbine operating mode. Examplesare permitting an Automatic Synchronizer or an Automatic Dispatch Systemto set the turbine reference, or selecting local operator automaticcontrol of the turbine (which includes hold/go action).

4. VALVE STATUS/TESTING/LIMITING - This group of buttons allows valvestatus information display, throttle/governor valve testing, and valveposition limit adjustment.

5. AUTOMATIC TURBINE STARTUP - This group of buttons is used inconjunction with a special DEH program which continuously monitorsimportant turbine variables, and which also may start up and acceleratethe turbine during wide-range speed control.

6. MANUAL OPERATION - These buttons allow the operator to manuallycontrol the position of the turbine valves from the Operator's Panel.The DEH PANEL task has no direct connection with this group of buttons.

7. KEYBOARD ACTIVITY - These buttons and keys allow numerical data to beinput to the DEH system. Such information may include requests fornumerical values via the display windows, or may adjust systemparameters for optimum performance.

The panel task 1112 responds to the buttons pressed on the operator'spanel 1130 by an operator of the DEH control system 1100. The controlpanel 1130 is shown in FIGS. 15 and 16. Referring now to FIGS. 31 and32, the interactions of the panel task 1112 are shown in greater detail.Pushbuttons 1110 are decoded in a diode decoding network 1912 whichgenerates contact inputs to activate the panel interrupt program 1156.The panel interrupt program scans the contact inputs and bids the paneltask 1112 whereby the pressed button is decoded and either the paneltask 1112 carries out the desired action or the logic task 1110 is bidor the visual display task 1134 is called to carry out the desiredcommand.

Automatic control of turbine speed and load requires a complex,interacting feedback control system capable of compensating for dynamicconditions in the power system, the boiler and the turbine-generator.Impulse chamber pressure and shaft speed from the turbine, megawattsfrom the generator, and throttle pressure from the boiler are used inthe controlled operation of the turbine.

In addition to the primary control features discussed above, the DEHsystem also contains provisions for high and low load limits, valveposition limit, and throttle pressure limit; each of these can beadjusted from the Operator's Panel. A number of auxiliary functions arealso available which improve the overall turbine performance and thecapabilities of the DEH system. Brief descriptions of these follow:

1. Valve position limit adjustment from the Operator's Panel.

2. Valve testing from the Operator's Panel.

3. Speed signal selection from alternate independent sources.

4. Automatic instantaneous, and bumpless operating-mode selection fromthe Operator's Panel.

5. A continuous valve position monitor and contingency-alert functionfor the operator during automatic control.

6. A digital simulation and training feature which allows use of theOperator's Panel and most of the DEH system at any time on manualcontrol, without affecting the turbine output or valve position. Thispowerful aid is used for operator and engineer training, simulationstudies, control system tuning or adjustment, and for demonstrationpurposes.

In order to achieve these objectives, the CONTROL task is provided withanalog inputs representing the various important quantities to becontrolled, and also is supplied with contact inputs and system logicalstates.

The control program 1012 and related programs are shown in greaterdetail in FIG. 33. In the computer program system, the control program1012 is interconnected with the analog scan program 1116, the auxiliarysync program 1114, the sequence of events interrupt program 1124 and thelogic task 1110. FIG. 34 shows a block diagram of the control program1012. The control program 1012 accepts data from the analog scan program1116, the sequence of events interrupt program 1124 and is controlled incertain respects by the logic program 1110 and the auxiliarysynchronizing program 1114. The control program 1012, upon receivingappropriate inputs, computes the throttle valve TV1-TV4 and the governorvalve GV1-GV8 outputs needed to satisfy speed or loud demand.

The control program 1012 of the DEH control system 1100 functions, inthe preferred embodiment, under three modes of DEH system control. Themodes are manual, where the valves GV1-GV8 and TV1-TV4 are positionedmanually through the hardwired control system and the DEH controlcomputer tracks in preparation for an automatic mode of control. Thesecond mode of control is the operator automatic mode, where the valvesGV1-GV8 and TV1-TV4 are positioned automatically by the DEH computer inresponse to a demand signal entered from the keyboard 1130, of FIG. 16.The third mode of control is remote automatic mode, where the valvesGV1-GV8 and TV1-TV4 are positioned automatically as in the operatorautomatic mode but use the automatic turbine startup program 1141 or anautomatic synchronizer or an automatic dispatch system for setting thedemand value.

SPEED SELECTOR FUNCTION

When operating a steam turbine, the single most important variable whichmust be controlled is shaft speed. During load operation, speedregulation is necessary to help the power system maintain linefrequency. During wide-range speed control, precise speed control isdoubly important to bring the unit to synchronous speed and to overcomecritical speed points at which excessive vibrations may cause a turbinetrip. To accomplish such demanding control objectives, it is necessaryto provide high-accuracy speed input signals to the control system sothat exact valve position outputs may be computed by the speedcontrollers.

The DEH Control System has three independent speed signals available;these are used to achieve the precision required in speed control. Thefirst of these (which is called the digital speed) is generated by amagnetic pickup, shaped and counted by specially-designed electronicprinted circuitry, and passed on to the DEH Control System in the formof a digital numerical value. The second speed signal (which is calledthe analog speed) is generated by an identical independent magneticpickup, processed in the analog packup circuitry for use there, andpassed on to the DEH system as the analog input. The third speed signal(which is called the supervisory speed) is also generated by its ownmagnetic pickup, processed by supervisory instrumentation methods, andpassed on to the DEH Control System as an analog input.

Referring now to FIG. 35, a block diagram of the DEH speedinstrumentation and computation interface is shown. A digital countingand shaping circuit 2010 described in the copending Ruether applicationSer. No. 412,513, referred to supra, generates the highly accuratedigital signal. The digital shaping and counting circuitry 2010 includesa magnetic pickup, a shaping and counting circuit which passes the datato the DEH computer in the form of a digital numerical value. The secondor analog speed signal is generated by high accuracy analog processingcircuitry 2012. The third or supervisory signal is generated by analogsupervisory instrumentation processing circuitry 2014 and transmitted toan analog to digital converter 2016 with the signal from the high gradeanalog processing circuitry 2012.

The digital signal from the digital shaping and counting circuitry 2010passes through a speed channel interrupt 2018 to a speed channeldecoding program 2020 as shown in FIG. 35. In this speed countingprogram 2020 an output quantity designated ICOURSE is the low rangecourse value used from about 0 to 1600 rpm, while the IFINE quantity isthe high range fine value used between about 1600 to 4500 rpm.

An analog to digital converter 2016 makes both the high precision analogsignals from the analog processing circuitry 2012 and the supervisorycircuitry 2014 available to the analog scan program 1116 which in turnprovides the represented speed values available to the speed selectionprogram 2022. The speed selection program 2022 compares the digitalspeed value and the high grade analog speed value with the supervisoryanalog speed value in order to determine whether both the digital valueand the high grade analog value are accurate or whether there is anydiscrepancy between the two. The supervisory speed value is generallynot accurate enough for speed control. Therefore, the speed selectionprogram 2022 makes use of the supervisory speed value to determine whichof the high grade speed values is accurate if they are not equal.

The speed selection function determines which of these available speedinputs should be used in the DEH Control System. If the speed selectionprocess concludes that the digital speed is reliable, then under allcircumstances it is used as the controlling speed signal because it isthe most accurate. If the selection process concludes that the digitalspeed is unreliable, the analog speed is used as the controlling speedsignal since it is of acceptable accuracy. If neither the digital northe analog speed signal is reliable, the speed selection function mustdisable the speed feedback control loop, because the supervisory speedis not of acceptable accuracy for controlling turbine speed response.

Although the supervisory speed is unacceptable for control requirements,it performs a valuable role in helping to detion process is the value WSwhich is used by all other programs in the DEH system.

The digital speed value from the digital shaping and counting circuitry2010 is used as the reference WS at 1076 if it is found to be accurateenough for control purposes. The high grade analog speed value from theanalog processing circuitry 2012 is utilized if the digital speed valueis not accurate enough for control purposes. If either of the high gradesignals becomes unreliable, appropriate monitor lamps on the controlpanel 1130 alert an operator to this fact.

If both the high grade analog and the high grade digital speed valuesbecome unreliable and if the DEH system 1100 is on wide range speedcontrol then a transfer takes place to the manual mode of control.However, if the turbine system 10 is on load control, the DEH system1100 opens the speed feedback loop bumplessly and continues on automaticcontrol with the remaining feedback loops intact.

SELECT OPERATING MODE FUNCTION

Input demand values of speed, load, rate of change of speed, and rate ofchange of load are fed to the DEH control system 1100 from varioussources and transferred bumplessly from one source to another. Each ofthese sources has its own independent mode of operation and provides ademand or rate signal to the control program 1020. The control task 1020responds to the input demand signals and generates outputs whichultimately move the throttle valves TV1 through TV4 and/or the governorvalves GV1 through GV8.

With the breaker 17 open and the turbine 10 in speed control, thefollowing modes of operation may be selected:

1. Automatic synchronizer mode -- pulse type contact input for adjustingthe turbine speed reference and speed demand and moving the turbine 10to synchronizing speed and phase.

2. Automatic turbine startup program mode -- provides turbine speeddemand and rate.

3. Operator automatic mode -- speed, demand and rate of change of speedentered from the keyboard 1860 on the operator's panel 1130 shown inFIG. 16.

4. Maintenance test mode -- speed demand and rate of change of speed areentered by an operator from the keyboard 1860 on the operator's controlpanel 1130 of FIG. 16 while the DEH system 1100 is being used as asimulator or trainer.

5. Manual tracking mode -- the speed demand and rate of change of speedare internally computed by the DEH system 1100 and set to track themanual analog back-up system 1016 as shown in FIG. 4 in preparation fora bumpless transfer to the operator automatic mode of control.

With the breaker 17 closed and the turbine 10 in the level mode control,the following modes of operation may be selected.

1. Throttle pressure limiting mode a contingent mode in which theturbine load reference is run back or decreased at a predetermined rateto a predetermined minimum value as long as a predetermined conditionexists.

2. Run-back mode -- a contingency mode in which the load reference isrun back or decreased at a predetermined rate as long as a predeterminedcondition exists.

3. Automatic dispatch system mode -- pulse type contact inputs aresupplied from an automatic dispatch system to adjust turbine loadreference and demand when the automatic dispatch system button 1870 onthe operator's panel 1130 is depressed.

4. Operator automatic mode -- the load demand and the load rate areentered from the keyboard 1830 on the control panel 1130 in FIG. 16.

5. Maintenance test mode -- load demand and load rate are entered fromthe keyboard 1860 of the control panel 1130 in FIG. 16 while the DEHsystem 1100 is being used as a simulator or trainer.

6. Manual tracking mode -- the load demand and rate are internallycomputed by the DEH system 1100 and set to track the manual analogback-up system 1016 preparatory to a bumpless transfer to the operatorautomatic mode of control.

The select operating mode function responds immediately to turbinedemand and rate inputs from the appropriate source as described above.This program determines which operating mode is currently in control bypeforming various logical and numerical decisions, and then retrievesfrom selected storage locations the correct values for demand and rate.These are then passed on to the succeeding DEH control programs forfurther processing and ultimate positioning of the valves. The selectoperating mode function also accommodates switching between operatingmodes, accepting new inputs and adapting the DEH system to the new statein a bumpless transfer of control.

Various contact inputs are required for raise and lower pulses, manualoperation, maintenance test, and so forth; these are handled by theSEQUENCE OF EVENTS interrupt program and the PLANTCCI subroutine, whichperforms a contact input scan. In addition, certain panel pushbuttonsaffect the operating mode selection; these are handled by the PANELINTERRUPT program and the PANEL task, which decode and classify thepushbuttons pressed. The LOGIC task then checks all permissiveconditions and current control system status, and computes theappropriate logical states for interpretation by the CONTROL task andthe SELECT OPERATING MODE program.

Referring now to FIG. 36, a block diagram is shown illustrating theselect operating mode function 2050. Contact inputs from plant wiring1126 activate the sequence of events interrupt program 1124 which callsthe plant contact input subroutine 1150, to scan the plant wiring 1126for contact inputs. Mode pushbuttons such as automatic turbine startup1141, automatic dispatch system 1170 and automatic synchronizer 1871activates the panel interrupt program 1156 which calls the panel program1112 for classification and which in turn calls upon the logic program1110 to compute the logic states involved. The logic program 1110 callsthe control program 1020 to select the operating mode in that program.

In FIGS. 37A and 37B a flow chart of the select operating mode logic isshown. As one example of mode selection referring to a path 2023, aftera statement 7000, provisions are made for a bumpless transfer from anautomatic or test mode to an operator mode. The bumpless transfer isaccomplished by comparing the computer outputs and the operator modeoutput signals for the governor valve GV1-GV4 positions. The DEH system1110 inhibits any transfer until the error between the transferringoutput and the output transferred is within a predetermined deadband(DBTRKS). Bumpless transfer is accomplished by the DEH control system1100 by comparing output from one mode of control of the governor valvesGV and the throttle valves TV and the same output from another outputmode controlling the same parameters. The flow chart of FIGS. 37A and37B shows mode selection for a complete operating system. In a hardwiredor analog control system, the analog parameter output, to be transferredto must continuously track the parameter output to be transferred from.This tracking method is expensive and cumbersome since it has to be donecontinuously and requires complex hardware. However, in a digitalsystem, such as the DEH control system 1100, the equating of the twoparameter outputs need be performed only on transfer. Therefore, greateconomy of operation is achieved.

SPEED/LOAD REFERENCE FUNCTION

In the DEH turbine controller, the speed/load reference is the centraland most important variable in the entire control system. The referenceserves as the junction or meeting place between the turbine speed orload demand, selected from any of the various operating modes discussedin the last section, and the Speed or Load Control System, which directsthe reference through appropriate control system strategy to the turbinethrottle and governor valves to supply the requested demand. FIG. 38 isa diagram which indicates the central importance of the reference in theDEH control system.

The speed/load reference function increments the internal turbinereference at the selected rate to meet the selected demand. Thisfunction is most useful when the turbine is on Operator Automatic, onthe AUTOMATIC TURBINE STARTUP program, or in the Simulator/Trainermodes. This is because each of these control modes requests unique ratesof change of the reference, while the remaining control modes, such asthe Automatic Synchronizer and the Automatic Dispatch System, move thereference in pulses or short bursts which are carried out in one step.The Runback and Throttle Pressure contingency modes use some of thefeatures of the reference function, but they bypass much of the subtlereference logic in their hurry to unload the turbine.

For these modes which request movement of the reference at a uniquerate, the reference function must provide the controlled motion. Notonly must the rate be ramped exactly, but the logic must be such that,at the correct time, the reference must be made exactly equal to thedemand, with no overshoot or undershoot. In addition, the referencelogic must be sensitive to the GO and HOLD states, and must start orstop movement instantly if requested to do so. Finally, the referencesystem must turn off the GO and HOLD lamps, if conditions dictate, bypassing on to the LOGIC task the proper status information to accomplishthis important visual indication feature.

The decision breaker function 1060, of FIG. 5, is identical to thespeed/load reference function 1060, of FIG. 38. A software speed controlsubsystem 2092 of FIG. 38, corresponds to the compare function 1062, thespeed reference 1066 and the proportional plus reset controller function1068, of FIG. 5. The software load control subsystem 1094, of FIG. 38,corresponds to the rated speed reference 1074, the turbine speed 1076,the compare function 1078, the proportional controller 1080, the summingfunction 1972, the compare function 1082, the proportional plus resetcontroller function 1084, the multiplication function 1086, the comparefunction 1090, the impulse pressure transducer 1088 and the proportionalplus reset controller 1092, of FIG. 5. The speed/load reference 1060 iscontrolled by, depending upon the mode, and automatic synchronizer 1080,the automatic turbine starter program 1141, and operator automatic mode1082, a manual tracking mode 2084, a simulator/trainer 2086, anautomatic dispatch system 2088, or a run-back contingency load 2090.Each of these modes increments the speed/load reference function 1060 ata selectd rate to meet a selected demand.

SPEED CONTROL FUNCTION

The speed control function positions the throttle and governor valves toachieve the existing speed reference with optimum dynamic and steadystate response. This is accomplished by using individualproportional-plus-reset controllers for throttle and governor valvespeed control, as shown in FIG. 39. The speed error between the turbinespeed reference and actual speed drives the appropriate controller,which then reacts by positioning the proper valves to reduce the speederror to zero. The speed controller outputs are low-limit checkedagainst zero and high-limit checked against the quantity HLS, which is akeyboard-entered constant set at 4200 rpm. This prevents the controllersfrom reaching a reset-windup condition which may inadvertently occur inodd circumstances. The speed controller output is then suitably rangedfrom 0 to 100 percent and sent downstream as the quantity SPD in theCONTROL task to the THROTTLE and GOVERNOR VALVE programs.

LOAD CONTROL FUNCTION

The load control function positions the governor valves to achieve theexisting load reference with optimum dynamic and steady state response.This is accomplished with a feedforward-feedback control system strategydesigned to stabilize interactions between the major turbine-generatorvariables: impulse chamber pressure, megawatts, shaft speed and valveposition. FIGS. 40 and 41 show the control system which satisfies theseobjectives.

The main feedforward path is represented by the turbine load referencevalue (REFDMD), which is computed by the operating mode selectionfunction described earlier. The feedforward variable (REFDMD) iscompensated with two feedback trim factors to account for frequency(speed) participation and megawatt mismatch. The speed compensation isprovided by a proportional feedback loop in which the droop regulationgain (GR1) is adjusted to yield rated megawatts correction for a 180 rpmspeed error. This speed feedback factor (X) is then summed with theturbine load reference (REFDMD) to produce the speed-corrected loadreference (REF1).

A special feature which has been incorporated in the speed feedback loopis a software speed-deadband; this non-linear function filters outhigh-frequency low-amplitude noise on the speed input signal, thuskeeping the load control system from responding to such meaninglessinformation. The width of the speed deadband may be adjusted from thekeyboard by setting the appropriate value into the constant SPDB.Another special feature of the speed deadband is the method ofimplementing this function in comparison with most standard controlsystems. The common way to incorporate the speed deadband in previoussystems is to allow speed errors greater than the width of the deadbandto enter the control system completely. This has been found to shockmany systems into oscillatory conditions which may have undesirableeffects. In the DEH Control System the speed error, when it is largerthan the deadband, is smoothly entered into the speed compensationfactor by a linear relationship. Thus the shock effect of a sudden speederror is removed completely.

The megawatt feedback loop provides a trim correction signal which isapplied to the speed-compensated load reference (REF1) in a product formto yield the speed-and-megawatt corrected load reference (REF2). Anadditional highly desirable feature of megawatt feedback in the DEHsystem is that with it the reference and demand display windows on theOperator's Panel are calibrated in actual megawatts when the loop is inservice. A proportional-plus-reset controller is used to reduce megawatterror to zero, with the loop providing a feedback factor (Y) whichfloats around unity (1.0) in performing its corrective action. As usual,high and low limits are provided to prevent reset windup and to boundthe range of megawatt compensation.

The load reference (REF2), now corrected for speed and megawatt errors,becomes the set point for the impulse pressure cascade feedback loop orthe direct demand for valve position, depending on whether the impulsepressure loop is in or out of service. REF2 is multiplied by a ranginggain (GR3) to convert to impulse pressure set point (PISP) in psi. Ifthe loop is in service, then a proportional-plus-reset controller isimplemented to drive the impulse pressure error to zero; as always, highand low limits restrict the range of variation of the controller toeliminate the possibility of reset windup. The final governor valve setpoint (VSP), whether it is generated by the feedback loop or directlyfrom the load reference (REF2), is then converted into a percent valvedemand (GVSP) by suitable ranging and is sent downstream in the controltask to the THROTTLE and GOVERNOR VALVE programs.

The load control function block diagram shown in FIGS. 65 and 65A is anexpansion of the load control, shown in FIG. 5, incorporating the speedloop subroutine and proportional control of function diagram of FIG. 11.

THROTTLE VALVE CONOTROL FUNCTION

The throttle valve control function (FIG. 42) computes the correct valueof the throttle valve analog output at all times. When the DEH system ison automatic control, this analog output actually positions the throttlevalves; when the DEH system is on manual control, this analog outputtracks the backup system preparatory to transfer to automatic control.

To accomplish its objective, the throttle valve control function mustinterrogate various turbine logical and numerical states, and proceed toact on the outcome of these decisions. There are five distinctsituations which must be detected by these logical and numericalinterrogations. A brief description of these follow; refer to Figure forthe method of performing these tests and the major actions taken.

1. The turbine is unlatched and in neither throttle nor governor valvecontrol. During this time the throttle valves are held closed by thethrottle valve control function.

2. The turbine is latched and in positive throttle valve control whilethe DEH system is in wide-range speed control. During this time thethrottle valve control function accepts the output of the speedcontroller (SPD) and positions the throttle valves accordingly.

3. The DEH system is in a transition period, transferring from throttleto governor valves during wide-range speed control. For this interval oftime, the throttle valves are still in positive control and the throttlevalve control function continues to accept the speed controller output(SPD) and positions the throttle valves accordingly.

4. The DEH system remains in the transition period of transferring fromthrotte to governor valve control; but now the governor valves are inpositive control. During this time the throttle valve control functiondrives the throttle valves to the wide-open position with a throttlevalve bias integrator (TVBIAS), which has a constant input (BTVO)incrementing the integrator.

5. The transition period is over and the transfer from throttle togovernor valve control is complete; the turbine is now on eitherwide-range speed control or on load control after having beensynchronized with the power system. During this time the throttle valvecontrol function keeps the throttle valves wide open.

GOVERNOR VALVE CONTROL FUNCTION

The governor valve control function (FIG. 43) computes the correct valuefor the governor valve analog output at all times. When the DEH systemis on automatic control, this analog output actually positions thegovernor valves; when the DEH system is on manual control, this analogoutput tracks the backup system preparatory to transfer to automaticcontrol.

To accomplish its objective, the governor valve control function mustinterrogate various turbine logical states and proceed to act on theoutcome of these decisions. There are five distinct situations whichmust be detected by these logical interrogations. A brief description ofthese follows; refer to Figure for the method of performing these testsand the major action taken.

1. The turbine is unlatched and in neither throttle nor governorcontrol. During this time the governor valves are held closed by thegovernor valve control function.

2. The turbine is latched and in positive throttle valve control whilethe DEH system is in wide-range speed control. During this time thegovernor valve control function drives the governor valves wide openwith a governor valve bias integrator (GVBIAS).

3. The DEH system is in a transition period, transferring from throttlevalve to governor valve control during wide-range speed operation. Forthis interval of time, the governor valve control function drives thegovernor valves to the closed position with the governor valve biasintegrator (GVBIAS). The governor valve control function then waits fora decrease in turbine speed and for the Analog Backup System to trackthe computer outputs.

4. The DEH system remains in the transition period but now the governorvalves are in positive control during wide-range speed operation. Duringthis time the governor valve control function accepts the output of thespeed controller (SPD) and positions the governor valves accordingly.

5. The main generator circuit breaker is closed and the DEH system is inload control. During this time the governor valve control functionaccepts the output of the load control system (GVSP) and positions thegovernor valves accordingly.

FIG. 67 shows a block diagram of the governor valve control functionwhich computes the position of the governor valve output at all times.

TURBINE OPERATION SIMULATION

In order to allow operators to become proficient in the operation of theDEH system 1100 without risking damage to a multimillion dollarturbine-generator system 10 a simulation subroutine 2110, in FIG. 64, isprovided during speed control. A similar subroutine 2111 is provided forsimulation of the turbine-generator system dynamics.

BUMPLESS TRANSFER

A flow chart path (FIG. 43) allows for the smooth and bumpless transferfrom governor valve control to throttle valve control and vice versa. Afunction 2102 tests whether a governor valve bias integrator GVBIAS hasreached zero. By forcing the DEH system 1100 to wait until the governorvalve bias integrator GVBIAS has reached zero a bumpless transfer fromgovernor to throttle valve control and vice versa is effectuated. Otherbumpless transfer features are considered elsewhere herein.

DEH SYSTEM PROGRAMS AUXILIARY SYNCHRONIZER (AUX SYNC) TASK

The program first checks the CONTROLLER RESET pushbutton on the DEHOperator's Panel; if the button is backlighted, the operator has notacknowledged computer return from a power failure or an out-of-synccondition. When the button is pressed, the AUX SYNC task proceeds tocarry out its functions.

The program checks three counters for timing. IVPL is incremented in1/10 sec steps as long as the VALVE POSITION LIMIT RAISE or LOWERbuttons are pressed. CADSUP is similarly incremented as long as theAutomatic Dispatch System (ADS) raise contact input is set. CADSDOWN isincremented while the ADS lower contact input is set. Finally, if theRUNLOGIC variable is set, AUX SYNC bids the LOGIC task to run.

The program then initiates a FORTRAN DO loop to check for normalexecution of the DEH system periodic tasks. Each entry in the arrayICOUNTER is incremented and tested against its maximum count (IMAX). IfICOUNTER has expired, it is reset to zero and transfer is made toappropriate portions of the remaining program. Otherwise the nextcounter is examined in the same way until all have been tested; at thistime the AUX SYNC task exits until the next bid from the Monitor.

When the first ICOUNTER expires, the CONTROL task is bid and a flag(ISCAN) is set for further action in both the AUX SYNC and the ANALOGSCAN tasks. When the second ICOUNTER expires, logical decisions are madeon ISCAN and INTSCAN to set up the necessary information to properlyexecute the ANALOG SCAN task. This task and the FLASH task are then bidto run.

When the third ICOUNTER expires, the AUTOMATIC TURBINE STARTUP (ATS)task is bid. In addition, the VISUAL DISPLAY task is bid if no key entryis being made on the Operator's Panel keyboard. The PLANTCCI subroutineis called if the constant PERCCI has been set non-zero from the keyboardto request a periodic contact input scan. Finally, when the fourthICOUNTER expires the ATS MESSAGE WRITER task is bid.

The AUX SYNC program communicates with the various counters, flags andvariables in the DEH system through the COMMON areas BETA, DELTA, ZETAand THETA. The program size is 135 words, the data pool size is 36words, and the task header size is 9 words, for a required minimumstorage of 180 locations. AUX SYNC is linked as a separate task and isloaded into the computer through the tape reader. The core area assignedto the task is from (14EO to 149F)₁₆ ; this is CO₁₆ (192₁₀) locations,thus allowing some room for expansion.

VALVE INTERRUPT PROGRAM

The VALVE TEST CLOSEPB is interrogated to determine if it was thepushbutton released. If so, the pushbutton flag is reset and the contactoutput holding the throttle valve in a test close position is reset. Ifnot, the VALVE TEST OPENPB is interrogated to determine if it was thepushbutton released. If so, the pushbutton flag is reset and the testanalog output (TESTAO) is checked to determine if it has been reduced tozero. If not, no further action is taken since the test is notcompleted. But if the test analog output is zero, then the counter(NVTEST) indicating which valve was being tested is reset to zero andthe contact output connecting this test signal to the governor valveservo amplifier is reset.

If neither the CLOSEPB nor the OPENPB had been released, then the VALVEINTERRUPT program concludes that it was a VALVE POSITION LIMIT RAISE orLOWER pushbutton; therefore, both of these are reset and return is madeto the Monitor interrupt handler indirectly through location OODF₁₆(0223₁₀) in the Monitor zero table.

ANALOG SCAN TASK

The ANALOG SCAN task is assigned priority level B₁₆ (11₁₀) and is bid bythe AUX SYNC task every 1/2 sec.

The ANALOG SCAN task communicates with other parts of the DEH systemthrough various COMMON areas. The BETA COMMON contains the variableFLGWRD which is set by the Monitor analog handler to indicate that theA/D converter is out of service. The converted base DEH system analoginputs are stored in the GAMMA COMMON area, while DELTA contains thearrays SLOPE and BINT for conversion of inputs to engineering units.Additional logic states are accessed via ZETA COMMON, while the ATSanalog inputs and control words are located in TAAI and TAADBUF.

The program first checks the value of ISCAN, which is set by the AUXSYNC program to indicate whether to scan base DEH inputs or ATS inputs.These groups are each scanned on alternate 1/2 sec; the AUX SYNC taskarranges the timing so that 1/2 sec prior to bidding the CONTROL task,the ANALOG SCAN task is directed to scan the inputs necessary for thecontrol system. The following 1/2 sec, while the CONTROL task isrunning, the AUX SYNC task arranges the timing so that the ANALOG SCANtask will scan a group of ATS inputs. This is done by setting ISCAN = 0for base DEH inputs and ISCAN = 1 for ATS inputs.

When ISCAN = 0, the Monitor analog handler is called to scan the 15 baseDEH inputs. The handler must be provided with a list of control words,one per input, which defines the hardware configuration of each inputwhich are stored in ADBUF1. The P2000 Monitor Reference Manual, TP043,describes the format and function of each bit in these words, butessentially these bits define the channel, bit, multiplexer word and A/Dgain setting for each input.

When the A/D converter completes the scanning of these inputs, the rawbit patterns are stored in a temporary buffer (VALBUF). The scan programthen executes a FORTRAN DO loop to process these inputs. The two inputsMW and PI are checked for sensor failure against absolute low and highlimits, and appropriate action is initiated if either failure occurs.

The remaining 10 base DEH inputs represent governor and throttle valvedemand from the analog backup system and the digital system, and theactual LVDT position of each governor and throttle valve. These inputsare not converted but are kept in their raw form until used by theappropriate program. The reason for this is that these quantites areused much less frequently than the above inputs. In addition, the formatof these inputs in engineering units is a percent value from 0 to 100;consequently, there is not much advantage to their conversion. However,these values are checked for low sensor limit, and if this occurs, theyare set to zero. A portion of the instructions to do this work arewritten in Assembly language to reduce the program size. The inputs forthe valve demands are stored in array ITVGV and the LVDT inputs arestored in arrays ITVGVSS.

The last action taken in this part of the ANALOG SCAN program is tocheck the A/D converter. The Monitor analog handlers set the variableFLGWRD if the A/D converter cannot be adjusted to the existing plantconditions; if this flag is set, the converter is said to be out ofservice and all feedback loops must be removed from the control system.

The variable ISCAN is reset to zero and a GO TO statement is executed;the transfer point depends on the value of INTSCAN, which is incrementedonce a second and runs from 1 to 10 before being reset back to 1.INTSCAN values 1, 3, 6 and 8 represent intervals of time when noaddditional work need be done, as can be seen on the timing chart ofFIG. 2. INTSCAN values of 2 and 7 (thus being 5 sec apart) transfer tostatement 200. Here a second counter (ISPAN) is incremented in steps of1; when ISPAN = 3, this represents a 15 sec interval and thus aSPAN/ADJUST call must be made. As this is done, the counter ISPAN is setback to zero.

When INTSCAN = 9, it is time to call for a group of temperature analoginputs; these are scanned in groups of 10, and there are 6 such groups.Thus, the counter NSYNC1 is incremented from 1 to 6 to indicate to theATS conversion program which group has been input at this time. Also,the variable NSYNC2 is set to -1 to indicate that temperatures arecoming in now. Finally, J is a pointer to the proper control words inthe ATS COMMON area ITAAI.

When INTSCAN = 4, the ATS miscellaneous inputs which are scanned every10 sec will be input. Statement 400 sets J to the proper pointer andsets NSYNC2 = -2 to indicate this fact.

When INTSCAN = 5 or 10, transfer is to statement 500 which sets up J topoint to the ATS 5 sec vibration inputs. A flag (BIDATSCV) is also setat this point so that the ATS CONVERSION task may be bid further on inthis program (note that this conversion task is bid every 5 sec).Finally, the Monitor analog handler is called with the proper pointer tocontrol word tables and buffer areas where the raw bit patterns arestored for the appropriate group of ATS inputs.

The ANALOG SCAN task size is 335 words, its data pool size is 89 words,and its header is 9 words for a required minimum storage of 433locations. ANALOG SCAN is linked as a separate task and loaded into thecomputer through the tape reader. The core area assigned to ANALOG SCANis (16DO to 188F)₁₆ ; this is 11CO₁₆ (448₁₀) locations, which allows afew spares.

LCCO SUBROUTINE

The subroutine is called only by the LOGIC task and thus is notreentrant. Arguments to the LCCO subroutine include three variableswhich indicate the appropriate action to be taken, and a pointer to atable of contact output words and bits which define the hardwareconnections for the quantities which must be set or reset.

The LCCO subroutine is designed so that a call from the LOGIC taskprovides a list of the variables necessary to evaluate whether or notcontact outputs should be actuated and, if so, whether they should beset or reset. Not all calls to LCCO involve the logical pushbuttonstate; in those cases this argument (LVIPB) is a dummy which satisfiesthe calling sequence but accomplishes no other significant action. Anexclusive-OR test is made on LV and LVX; if they are alike, no furtheraction is taken. If they are different, this means contact outputs mustbe actuated.

LOGIC TASK

The LOGIC task is organized as a series of small subprograms which areexecuted sequentially and which address themselves to particular aspectsof the total DEH Control System logical operation. The subprograms arein some cases quite simple, as when monitor lights are turned on or off,and in other cases they are quite complex, as when it is necessary toaccount for many permissive conditions to allow feedback loops to be putinto service.

FLIP-FLOP FUNCTION

The flip-flop is a basic building block of most logic systems, whetherthe system be of hardware or of software construction. A flip-flop isessentially a memory element which may be set or reset by other logicalelements to achieve a desired result. The flip-flop has two inputterminals, one for setting and one for resetting (or clearing), and oneoutput terminal, which indicates the state of the flip-flop.

The operation of the flip-flop is as follows. A logically true signal atthe set terminal results in a logical true signal at the outputterminal, while a logically true signal at the reset terminal produces alogical false signal at the output terminal. Simultaneous logically truesignals at both the set and reset terminals yield a logical false signalat the output terminal, thus providing the reset terminal withprecedence over the set terminal. Simultaneous logically false signalsat both the set and reset terminals yield no change at the outputterminal; that is, the output stays at whatever state it had been, thusproviding the memory feature of the flip-flop.

The flip-flop function has been incorporated into the DEH system with aFORTRAN FUNCTION statement, thus allowing evaluation of the flip-flopelement anywhere in the LOGIC task as an in-line statement.

MAINTENANCE TEST

The MAINTENANCE TEST system is activated by a two-position key-lockswitch on the Operator's Panel. The function of this switch is to allowtuning or adjusting of certain constants in the DEH Control System, orto allow operation of the DEH system in a simulation mode for trainingpurposes. When such tests are to be performed, the maintenance test keyis moved to the right position; this immediately switches the turbine tomanual control by a wired connection and sets a contact input to the DEHsystem. The LOGIC task then reacts in three ways: first, a contactoutput is set which turns on a monitor lamp above and to the right ofthe maintenance test switch; second, another contact output is set whichrequests transfer to manual as a backup to the wired connection; andthird, the manual-tracking portion of the DEH Control System isdisabled.

When the maintenance test action is completed and the test switchreturned to the off position, the LOGIC task resets the two contactoutputs to turn off the maintenance test lamp and to release the requestfor manual control. In addition, this part of the program enables themanual-tracking system by resetting the turbine REFERENCE and DEMAND tozero and allowing the normal control programs to run.

TURBINE SUPERVISION OFF LOGIC

The logical state (TSOFF) may be set by either the panel pushbuttonrepresented by TURBSPOF or by the A/D converter out of service as givenby VIDAROS. The pushbutton state (TURBSPOF) is generated by the PANELtask while VIDAROS is generated by the ANALOG SCAN task. A call to theLCCO subroutine is then made to update the pushbutton lamp status.

OPERATION AUTOMATIC LOGIC

The state of manual or automatic operation of the DEH system is actuallydetermined by circuitry in the analog backup system, and the DEHprograms simply respond to these states. When the DEH system is inmanual control, the analog backup system ignores the computer outputsignals and positions the valves according to its up/down countercircuitry. Conversely, when the DEH system is in automatic control, theanalog backup system uses the computer outputs to position the valvesand adjusts its up/down counter to track the computer outputs.

When transfer is made to manual, either by pushbutton or computerrequest, the analog backup system opens contacts carrying the computeroutputs to the valves and simultaneously closes contacts carrying backupsystem outputs to the valves. In addition, a contact input is sent tothe DEH system LOGIC task indicating manual operation. When transfer ismade to automatic control by pressing the OPERATOR AUTOMATIC pushbutton,and assuming that the computer system is tracked and ready forautomatic, the analog backup system opens contacts carrying its ownsignals to the valves and simultaneously closes contacts carrying thecomputer outputs to the valves. The operator automatic logic thus merelyupdates internal computer variables to the state of manual or automaticcontrol as determined by the backup system.

In updating the DEH system programs to the existing control state, theinternal operator automatic variable (OA) is set to the logical inverseof the manual contact input represented by TM. Then a decision is madeto determine if the system has just been switched to automatic bycomparing OA and its last value (OAX). If automatic has just occurred,ready tracking flags are reset; if not, no action is taken. In eithercase, the last value (OAX) is set to the current automatic state (OA)for use in the next bid of the LOGIC task.

GO LOGIC

When the DEH system is on operator automatic control, the turbinespeed/load (DEMAND) is entered from the keyboard. The operator then mayallow the turbine reference to adjust to the demand by pressing the GOpushbutton. When the operator does this, the GO lamp is turned on andlogical states are set to begin moving the reference in the CONTROLtask. When the reference equals the demand, the GO lamp is turned off.The GO logic detects the various conditions affecting the GO state andsets the status and lamp accordingly.

The GO pushbutton (GOPB), which is updated by the PANEL task, is the setsignal for the GO flip-flop. The reset or clear signal, which willoverride the set signal, can occur from a number of different conditonsas follows: the HOLD pushbutton (HOLDPB) as updated by the PANEL task, acomputed hold condition (HOLDCP) as set by the CONTROL or LOGIC tasks,the DEH system not being in operator automatic control (OA) or in themaintenance test condition (OPRT) (during which the system may be usedas a simulator/trainer), or the condition in which the reference hasreached the demand and the CONTROL task sets the GOHOLDOF state to clearthe GO lamp.

HOLD LOGIC

When the DEH system is an operator automatic control, the turbinespeed/load (DEMAND) is entered from the keyboard. The operator may theninhibit the turbine reference from adjusting to the demand by pressingthe HOLD pushbutton. When the operator does this, the HOLD lamp isturned on and logical states are set to prohibit the reference frommoving in the CONTROL task. The HOLD logic detects the variousconditions affecting the HOLD state and sets the status and lampaccordingly.

The HOLD pushbutton state (HOLDPB), which is set by the PANEL task, orthe hold state (HOLDCP) computed by the CONTROL or LOGIC tasks, acts asthe set signal for the HOLD flip-flop. The reset or clear signal, whichwill override the set signal, can occur from a number of differentconditions as follows: the DEH system not being on operator automaticcontrol (OA) or in the maintenance test condition (OPRT) (during whichthe system may be used as a simulator/trainer), the GO fip-flop beingset and thus overriding the HOLD state, or the condition in which thereference has reached the demand and the CONTROL task sets the GOHOLDOFstate to clear the HOLD lamp. The HOLD logic program then resets thecomputed hold state (HOLDCP) and the GOHOLDOF state, so that they may beused in future decisions by the CONTROL and LOGIC tasks.

GOVERNOR CONTROL LOGIC

Control of turbine steam flow with the governor valves is requiredduring speed and load control. Normally governor control is initiatedwhen the turbine has been accelerated to near synchronous speed, afterwhich the unit is brought up to synchronous speed, synchronized and thenloaded with the governor valves as the normal mode of operation.

The governor control logic detects turbine latch and unlatchingconditions, transfer from throttle valve to governor valve control, andmanual operation of the governor valves. When any of these conditionsoccur, the governor logic must align the DEH system to the appropriategovernor control state.

The governor control flip-flop (GC) may be set by a number ofconditions, the most common of which occurs on automatic control whenthe operator presses the transfer TV/GV pushbutton (TRPB). Assuming thatthe governor valves are at their maximum open position as indicated byGVMAX and that the automatic turbine startup mode (ATS) is not selected,then the governor flip-flop will be set. An alternate path for settingthis flip-flop occurs if the automatic turbine startup program (ATS)requests transfer via the logical variable ATSTRPB. In addition, whenthe throttle valves reach about 90 percent position, a contact input(THI) is activated by the analog backup system, and this contact setsthe GC flip-flop. This last case occurs when the turbine is a manualcontrol. Finally, the governor control flip-flop is reset when theturbine latch contact input (ASL) is released.

Following the GC flip-flop, a decision is made to determine if thesystem has just switched to governor control by comparing GC with itslast state (GCX). If transfer has just occurred, the turbine speed (WS)at this instant is saved as WSTRANS, the speed at throttle/governorvalve transfer. This value is used in the CONTROL task for a specialvalve position control logic decision. The last operation in thegovernor control program is to call the LCCO subroutine to update the GClamp.

THROTTLE VALVE CONTROL LOGIC

Control of turbine steam flow with the throttle valves is required whenthe turbine is initially rolled and during speed control up to the pointof transfer to governor valve control. After this the throttle valvesare kept wide open during normal operation. The throttle control logicdetects turbine latch and unlatching conditions, transfer from throttleto governor valve control, and manual operation of the throttle valves.When any of these conditions occur the throttle logic must then alignthe DEH system to the appropriate throttle control state.

The throttle control state (TC) is simply the logical inverse of thegovernor control state (GC) when the turbine is latched. However, thethrottle control lamp flip-flop (TCLITE) may be set by either TC or bymanual operation (TM) while the throttle valves are below 90 percentopen as indicated by the contact input (THI) not being set. The TCLITEflip-flop is reset by the contact input (THI) indicating throttle valveswide open or by the turbine latch contact input (ASL) not set.

The throttle control logic also indicates that the transfer fromthrottle to governor valve state (TRTVGV) is underway when governorcontrol (GC) exists but the throttle valves are not yet wide open. Inaddition, the transfer complete state (TRCOM) is set when the throttlevalves are wide open on governor control as indicated by THI. Finally,the program sets various contact outputs to pass this information on tothe plant and operating personnel by calling the LCCO subroutine.

TURBINE LATCH LOGIC

Before the turbine can be rolled and accelerated, it must bemechanically latched; this means the hydraulic fluid system must beprepared to move the throttle and governor valves, and a series ofsafety features as described in the turbine instruction book must besatisfied. After the turbine is latched, if unlatching should occur atany future time during speed or load control, then the control systemmust trip the turbine and close all valves immediately. The turbinelatch logic detects latching or unlatching, and instantly sets theturbine reference and the control system to the proper states. Adecision is made to determine if the turbine has just unlatched bycomparing the current latch state (ASL) with the last state (ASLX). Ifunlatched has just occurred, then the DEH turbine reference given byREFDMD, the demand given by ODMD, and the speed integral controllergiven by RESSPD are immediately reset to zero. If the turbine has notunlatched, then a decision is made to determine if the turbine has justlatched by a similar comparison of ASL and ASLX. If the unit has justlatched, the DEH reference (REFDMD) and demand (ODMD) are set to theexisting speed so that the control system may "catch the unit on thefly" should it be decelerating. The speed integral controller (RESSPD)is set to a zero value, from which point the control system will act tocontrol the throttle valves.

BREAKER LOGIC

The necessary and sufficient condition which must be satisfied whentransferring from speed to load control is that the governor valveanalog output must remain constant. This may be expressed as:

    GVAO.sub.LOAD = GVAO.sub.SPEED                             (1)

The computed values for these outputs may be written by referring toFIG. 23. This diagram shows the path taken by the CONTROL program oninitial load control, when the megawatt and impulse pressure feedbacksare out of service, and on speed control prior to breaker closing. Theexpressions for the two governor valve analog outputs given in Equation(1) above follow.

    GVAO.sub.LOAD = GR8 * GVPOS

    GVAO.sub.SPEED = GR7 * SPD

These may be substituted into Equation (1 ) and solved for the governorvalve position (GVPOS) in terms of the governor valve speed position(SPD) and ranging gains (GR7 and GR8). ##EQU2##

The required position (GVPOS) may in turn be related to the governorvalve set point (GVSP) and the governor valve characterization curve.This relationship follows. ##EQU3## POS(2) and SP(2) are points on thevalve characterization and represent the slope of the first segment ofthe curve. Substitution of Equation (3) into (2) and solution for GVSPyields the required set point for correct valve position. ##EQU4##

Referring to the load control system an expression for the governorvalve set point can be written in terms of additional computedquantities as follows: ##EQU5## VSP is the governor valve set point inpsi and GR4 is a ranging constant to convert to percent position.Substitution of Equation (5) into (4) produces the necessary value ofVSP. ##EQU6##

Note that immediately after synchronizing, the impulse pressure loop isout of service. In this case, then the governor valve set point (VSP) inpsi is identical to the impulse pressure set point (PISP) in psi. Thisis given below.

    VSP = PISP                                                 (7)

Substitution of Equation (7) into (6) yields the required value of PISP.##EQU7## Now the impulse pressure set point (PISP) can be related to themegawatt set point (REF2) as follows:

    PISP = GR3 * REF2                                          (9)

Gr3 is a ranging gain which converts megawatts to psi. Substitution ofEquation (9) into (8) allows computation of REF2. ##EQU8##

Note that at the instant of synchronization, the megawatt feedback loopis out of service and that the speed error is essentially zero(otherwise the unit would not have been synchronized). Thus, theexpression for the turbine reference is:

    REFDMD = REF2                                              (11)

Substitution of Equation (11) into (10) yields the desired result:##EQU9##

Equation (12) thus gives the required value which must be set into theturbine reference when the main breaker closes to maintain governorvalve position on transfer from speed to load control. When this isadded to the throttle-pressure modified initial megawatt pickupdiscussed above, the DEH Control System will make a smooth transfer fromspeed to load control with no potential motoring action by the turbine.

As shown in FIG. 24, the main generator breaker contact input (MGB) setsthe breaker flip-flop (BR), while loss of either MGB or the latchcontact input (ASL) resets the BR flip-flop. Then a test is made todetermine if the breaker just closed by comparing BR with its last state(BRX) as indicated by the leading edge of the BR pulse. If the breakerjust closed, then the initial megawatt pickup (MWINIT) modified bythrottle pressure ratio is computed as discussed above, the equivalentload governor position as given in Equation (12) is computed, and theseare added together to form the new load REFERENCE and DEMAND.

If the breaker did not close, then BR and BRX are tested to see if thebreaker opened as indicated by the trailing edge of the BR pulse. Ifthis is the case, the turbine REFERENCE and DEMAND are set tosynchronous speed, and logical flags set to rerun the LOGIC task toupdate the DEH system status. The final operation in the program then isto set the last states (MGBX and ASLX) to the current values of MGB andASL for succeeding bids of the LOGIC task.

THROTTLE PRESSURE CONTROL LOGIC

Control of throttle pressure in a fossil fired power plant is primarilya function of the boiler control system. Traditional turbine controlpractice is to react defensively to throttle pressure variations suchthat protection of the turbine is guaranteed. The DEH Control System isdesigned to detect throttle pressue below a set point and to runback theturbine reference at a preselected rate until the throttle pressurecondition is corredted. For this purpose, the throttle pressure detector112 of FIG. 1, transmits a signal to the DEH computer which is comparedto a predetermined pressure set by keyboard 1816 entry on the Operator'sPanel 1130. The throttle pressure control logic allows the throttlepressure controller to be placed in service or to be taken out ofservice by the operator when the turbine is on automatic control. Inaddition, this logic will automatically remove the loop from serviceunder certain contingency conditions or when the turbine is in speedcontrol.

The throttle pressure control flip-flop (TPC) may be set by the throttlepressure pushbutton (TPCPB) on the Operator's Panel or by the analogbackup system having its throttle pressure controller in service priorto transfer to automatic control; this latter case is given by the laststate (MANTPCX) of the contact input (MANTPC) being set while in manualcontrol. The TPC flip-flop is reset by a number of conditions; the panelpushbutton (TPCPB) when the loop is in service, breaker (BR) open,manual operation (TM), throttle pressure transducer failure (TPTF) whichis a contact input from the backup system, the analog-to-digitalconverter out of service (VIDAROS), or an attempt to put the loop inservice when the existing throttle pressure (PO) is below the set point(POSP). After evaluation of the TPC flip-flop, the program calls theLCCO subroutine to place the throttle pressure contact outputs in thecorrect state. Then the last values of the manual control and throttlepressure circuit are updated.

MEGAWATT FEEDBACK LOGIC

To place the loop in service bumplessly, it is necessary to maintainconstant governor valve position while inserting the megawattproportional-plus-reset controller in the control system computations.This means that the integrator in this controller must be instantly setto the proper value, the reference must be reset to that value whichwill yield no change in governor valve position, and proper account mustbe taken of the speed feedback effect at the instant of putting the loopin service. A derivation of the equations necessary to guarantee theseconditions follows.

REF2 is effectively the governor valve set point which must remain fixedin placing the loop in service, REFDMD is the turbine reference, X isthe speed feedback effect and REF1 is the speed modified reference. Whenthe loop is placed in service, the proper values of Y, the megawattfeedback factor, and RESMW, the megawatt integrator, must be computed,and REFDMD then readjusted to produce exactly the same value for REF2 toyield bumpless transfer. The necessary and sufficient condition forbumpless transfer then is that REF2 before and after the switching mustbe identical, as shown in Equation (13).

    REF2.sub.IN = REF2.sub.OUT                                 (13)

The value of REF2 before the switch is retained in computer memory,whereas the expression for REF2 after the loop is in may be determinedresult follows.

    REF2.sub.IN = Y * REF1.sub.IN                              (14)

Immediately after the switch, the value of REF1 must equal the existinganalog input representing megawatts (MW), so that the integrator sees azero error. Thus, an equation for this condition is:

    REF1.sub.IN = MW                                           (15)

Substituting Equations (13) and (15) into (14) and solving for therequired value of the megawatt factor (Y) and therefore the megawattintegrator output (RESMW) yields the following result: ##EQU10##

Finally, to guarantee that the transfer will be bumpless the new valueof REFDMD must be computed as follows.

    REF1.sub.IN = REFDMD.sub.IN + X                            (17)

Substituting Equation (15) into (17) and solving for REFDMD completesthe required derivation.

    REFDMD.sub.IN = MW - X                                     (18)

The steps in the computation may be summarized: compute the new value ofY and RESMW from Equation (16), compute the new value of REFDMD fromEquation (18), set the megawatt integrator last input (RESMWX) to zero,and place the loop in service.

To remove the megawatt loop from service bumplessly, a similar set ofcomputations must be followed. The necessary and sufficient conditionfor bumpless transfer is to retain a constant value for REF2 as follows.

    REF2.sub.OUT = REF2.sub.IN

The value of REF2 before the switch is retained in computer memory,whereas the expression for REF2 after the switch may be determined asgiven below.

    REF2.sub.OUT = REF1.sub.OUT

Immediately after the switch, the value of REF1 must equal the value ofREF2 before the switch, since the megawatt loop is now out of service.

    REF1.sub.OUT = REF2.sub.IN                                 (19)

Finally, to guarantee the bumpless transfer, the new value of thereference REFDMD must be computed to satisfy Equation (19).

    REF1.sub.OUT = REFDMD.sub.OUT + X                          (20)

Substituting Equation (19) into (20) and solving for REFDMD yields thefinal result.

    REFDMD.sub.OUT = REF2.sub.IN - X                           (21)

Thus to take the megawatt loop out of service, the reference is reset tothe value given in Equation (21) and the monitor lamp indication isreset.

The megawatt pushbutton, represented by MWIPB and updated by the PANELprogram, sets the megawatt flip-flop (MWI), while this flip-flop may bereset by a number of conditions as follows: the main breaker (BR) open;a megawatt transducer failure (MWTF), which is a contact input set bythe analog backup system; a valve position limit condition as indicatedby VPLIM; an analog input failure (AIFAILMW) of the megawatt feedbacksignal as set by the ANALOG SCAN program; or the analog-to-digitalconverter out of service (VIDAROS). After evaluation of the megawattflip-flop, decisions are made to determine if the megawatt loop has justbeen put into service or just taken out of service, assuming that themain breaker (BR) is closed. If the loop has just been put in, asindicated by the leading edge of the MWI pulse, then the bumplesstransfer computations listed in Equations (16) and (18) are executed. Ifthe loop has just come out of service, as indicated by the trailing edgeof the MWI pulse, then the bumpless transfer computation listed inEquation (21) is executed. In both cases a call to the LCCO subroutineis made to place the megawatt lamp and two status contact outputs forthe megawatt loop in the proper state.

IMPULSE PRESSURE FEEDBACK LOGIC

To place the impulse pressure loop in service bumplessly, it isnecessary to maintain the governor valves constant while inserting theimpulse pressure proportionalplus-reset controller in the control systemcomputations. This means that the integrator in the controller must beinstantly positioned at the proper value. Depending on whether themegawatt feedback loop is in service at this time, one of the followingtwo sets of derivations will be appropriate.

GR3 is a ranging constant which converts the megawatt reference value(REF2) to an impulse pressure set point (PISP) while IPI is the impulsepressure flip-flop. The analog input (PI) is the actual impulse pressureat the instant of placing the loop in service, RESPI is the impulsepressure integrator, and VSP is the governor valve set point. When theloop is put in service, both the integrator values (RESMW and RESPI)must be instantly recomputed to hold the governor valve set point (VSP)constant. Thus to remain bumpless, the following expression must hold.

    VSP.sub.IN = VSP.sub.OUT

The value of VSP before the switch is retained in computer memory,whereas after the loop is in service, the value of VSP will be given bythe integrator (RESPI). Therefore this integrator output must beinstantly set to the value of VSP.

    RESPI = VSP.sub.OUT

The additional requirement is that the impulse pressure set point (PISP)be identical to the existing impulse pressure analog input at theinstant of switching so that the integrator sees a zero error. This issatisfied as follows.

    PISP.sub.IN = PI                                           (23)

The computed value for PISP now may be written to determine what changesmust be made to the megawatt integrator.

    PISP = GR3 * REF2.sub.IN                                   (24)

The value of REF2 in turn may be determined in terms of REF1, which doesnot change when the impulse pressure is switchhed in since REF1 isupstream of the megawatt loop.

    REF2.sub.IN = Y * REF1                                     (25)

Substituting Equations (23) and (24) into (25), and remembering that themegawatt correction factor (Y) and the megawatt integrator output(RESMW) are equal, the new value which must be given to RESMW may besolved for as follows: ##EQU11## The steps in the computation to placeimpulse pressure feedback into service when the megawatt loop is alreadyin service may be summarized: compute the new value of the impulseintegrator from Equation (22), set the last value of the impulseintegrator input (RESPIX) to zero, compute the new value of the megawattintegrator from Equation (26), and place the loop in service.

To remove the impulse pressure feedback from service bumplessly, asimilar set of computations must be followed. The necessary andsufficient condition is to hold the value of VSP constant as follows:

    VSP.sub.OUT = VSP.sub.IN                                   (27)

The value of VSP before the switch will be retained in computer memory,whereas the value of VSP after the switch can be determined when theloop is out.

    VSP.sub.OUT = PISP                                         (28)

The set point (PISP) can in turn be computed as follows:

    PISP = GR3 * REF2                                          (29)

Finally, REF2 may be determined from REF1 which does not change since itis upstream of the megawatt integrator.

    REF2 = Y * REF1                                            (30)

Substituting Equations (27), (28) and (29) into (30), and rememberingthat the megawatt correction factor (Y) and the megawatt integrator(RESMW) are equal, the new value which must be given to RESMW may besolved for as follows: ##EQU12## The steps in the computation to removethe impulse pressure feedback from service when the megawatt loop is inservice are to compute the new value of the megawatt integrator fromEquation (31) and then place the loop out of service.

The above set of computations hold for switching the impulse pressureloop while the megawatt loop is in service. The situation issignificantly different when the megawatt loop is out of service, sincethen the reference must be reset to maintain a bumpless transfer. To putthe impulse pressure loop in service bumplessly, it is necessary, asalways, to keep the governor valve set point constant.

    VSP.sub.IN = VSP.sub.OUT

Again, the value of VSP before the switch will memory. in computermemory. The remaining equations describing the system after the switchmay be derived with results as follows:

    RESPI = VSP.sub.OUT

    PISP = PI

    PISP = GR3 * REF2

    REF2 = REF1

    REF1 = REFDMD + X                                          (32)

Solving this set of equations for the new value of REFDMD yields therequired condition. ##EQU13## Thus, to summarize, when placing impulsepressure feedback in service with the megawatt loop out of service, itis necessary to set the impulse integrator (RESPI) to the value given inEquation (32), reset the last input to this integrator (RESPIX) to zero,compute the new reference REFDMD from Equation (33), and place the loopin service.

The last case to cover is that of removing the impulse pressure loopwhen megawatt feedback is out of service. Once more the governor valvesmust remain constant to assure bumpless transfer, as indicated below.

    VSP.sub.OUT = VSP.sub.IN

As always, the value of VSP prior to the switch will be in computermemory. The set of equations describing the computations may be writtenas follows:

    VSP.sub.OUT = PISP

    PISP = GR3 * REF2

    REF2 = REF1

    REF1 = REFDMD + X

Solving this set of equations for the new value of REFDMD yields therequired condition. ##EQU14## Thus, REFDMD is computed according toEquation (34), the impulse pressure loop is removed, and the transferproceeds bumplessly.

The impulse pressure pushbutton, represented by IPIPB and updated by thePANEL program, sets the impulse pressure flip-flop (IPI), while a numberof conditons may reset the flip-flop as follows: the main breaker (BR)open; a valve position limiting conditon as indicated by VPLIM; ananalog input failure (AIFAILPI) for the impulse pressure feedback signalas set by the ANALOG SCAN task; the analogto-digital converter out ofservice (VIDAROS); or a contact input (SIO) to set impulse pressure outof servie when in the automatic dispatch system (ADS) mode. Afterevaluation of the impulse pressure flip-flop (IPI), decisions are madeto determine if the loop has just been put into service or just takenout of service assuming that the main breaker (BR) is closed. If theloop has just come in, as indicated by "the leading edge of the IPIpulse," then the bumpless transfer computations discussed and derivedabove are evaluated. If the loop has just come out, as indicated by "thetrailing edge of the IPI pulse," then again appropriate bumplesstransfer conditions are evaluated as discussed above. An additionaldecision is made on MWI as to whether or not the megawatt feedback loopis in service. As derived above, the form of the bumpless transfercomputations depends on the state of the megawatt loop. After allexpressions are evaluated, calls are made to the LCCO subroutine toplace the impulse pressure lamp and two status contact outputs in theproper state.

SPEED FEEDBACK LOGIC

The speed feedback loop is critically important when the turbine is onautomatic speed control, and is of somewhat less importance on loadcontrol. Without speed feedback on automatic speed control, the DEHsystem must reject to manual operation, while on automatic load controlthe DEH system merely removes the speed feedback loop from service. Theoperator may place the speed loop back in service after it has beenrejected by pressing the speed loop pushbutton, providing the speedinputs have in the meantime been corrected and are again valid.

Once the speed feedback loop is in service, the operator cannot take itout of service, since standard turbine control practic requires speed inservice at all times if the input signals are valid. Thus when the loopis in service, pressing the pushbutton is ignored. The only mechanismfor taking the loop out of service is by automatic action of the DEHsystem programs when a speed transducer failure occurs. The speedfeedback logic program responds to those conditions which will activateor deactivate the speed loop, whether the conditions be an operatorpushbutton request or automatic rejection by the transducer failure.

AUTOMATIC SYNCHRONIZER LOGIC

The auto sync flip-flop (AS) may be set by the auto sync pushbutton(ASPB) or by the automatic turbine startup program request (ATSASPB),provided in both cases that the unit is on automatic control (OA), thebreaker (BR) is open, the turbine is on governor control (GC), and theautomatic synchronizer equipment permissive contact input (ASPERM) isset. Otherwise the AS flip-flop will be reset. Decisions are then madeto determine if the AS flip-flop has just come on. If AS just came on,the temporary variable (T3) is set to indicate a remote control transferfor later logic programs. Then a call is made to the LCCO subroutine toset the auto sync lamp to the correct state; arguments in the callconsist of the current state of AS, the last state (ASX), the auto syncpushbutton state (ASPB) which must be aligned with the AS flip-flop, anda pointer (N9) to a table of contact output words and bits which defineconnections to the auto sync lamp.

Decisions must be made in the auto sync logic program, when the AS modehas been selected, to detect whether the automatic synchronizingequipment is sending raise or lower pulses to the DEH system. Thus, ifthe leading edge of the ASUP contact input pulse has just come on, thenthe logical variable ASINC is set so that the CONTROL task may incrementthe turbine reference by one rpm. Similarly, if the leading edge of theASDOWN contact input pulse has just come on, then the logical variable(ASDEC) is set so that the CONTROL task may decrement the turbinereference by one rpm. Finally, last values (ASUPX and ASDOWNX) areupdated to the current states (ASUP and ASDOWN) in preparation forfuture bids of the LOGIC task.

AUTOMATIC DISPATCH LOGIC

The automatic dispatch flip-flop (ADS) may be set by the automaticdispatch button (ADSPB), which is updated by the PANEL program,providing the unit is on automatic control (OA), the breaker (BR) isclosed, and the automatic dispatch permissive contact input (ADSPERM) isset. Otherwise the ADS flip-flop will be reset. Decisions then are madeto determine if the ADS flip-flop has just come on. If ADS just came on,the temporary variable (T3) is set to indicate a remote control transferfor later logic programs. Then a call is made to the LCCO subroutine toset the ADS lamp to the correct state; arguments in the call consist ofthe current state of ADS, the last state (ADSX), the automatic dispatchbutton (ADSPB) which must be aligned with the ADS flip-flop, and apointer (N10) to a table of contact output words and bits which defineconnection to the ADS lamp.

Additional decisions must be made in the ADS logic program, when the ADSmode has been selected, to detect whether the ADS equipment is sendingraise or lower pulses to the DEH system. Thus if the leading edge of theADSUP contact input pulse has just come on, then a flip-flop (CADSUP) isset to start a counter which is handled by the AUX SYNC program. As longas CADSUP is set the AUX SYNC will count in 1/10 sec increments, thusdetermining the length of time the raise pulse is on. When the trailingedge of the ADSUP contact input pulse is detected, this means the raisecontact has been released; this then resets the CADSUP flip-flop and theAUX SYNC program will stop counting. Finally, a logical state (ADSINC)is set so that the CONTROL task may raise the turbine reference by anamount proportional to the CADSUP counter. Identical checks and logicaldecisions are made with respect to the ADS lower contact input(ADSDOWN), after which last values of both ADSUPX and ADSDOWNX areupdated with the current state of ADSUP and ADSDOWN in preparation forfuture bids of the LOGIC task.

AUTOMATIC TURBINE STARTUP LOGIC

As shown in FIG. 29, the automatic startup flip-flop (ATS) may be set bythe pushbutton (AUTOSTAR), which is updated by the PANEL task, providedthe turbine is on automatic control (OA), the main breaker (BR) is notclosed, and the turbine supervision off pushbutton (TURBSPOF) has notbeen pushed. Otherwise the ATS flip-flop will be reset by the lack ofany of these conditions or by the automatic startup program itselfthrough the variable SSPROA if the program detects improper conditionsfor startup.

Decisions are then made to determine if the ATS flip-flop has just comeon. If so, a temporary logical variable (T3) is set to indicate a remotecontrol transfer for later logic programs. A decision is also made todetermine if the ATS flip-flop has just gone off. If this is the case,then a group of logical variables used in the ATS program must be reset.In addition, certain DEH system conditions must be aligned properly;these include the auto sync pushbutton (ASPB), which may have been setby the ATS program, and the reference/demand windows on the DEHOperator's Panel, which may have been left in an unequal state by thestartup program. These conditions are cleared by setting RUNLOGIC torequest another bid of the LOGIC task. Finally a call is made to theLCCO subroutine to set the ATS lamp to the proper state. Arguments inthe call are the current state of ATS, the last state (ATSX), the autostart pushbutton (AUTOSTAR) which must be aligned with ATS, and apointer (N11) to a table of contact output words and bits which definethe hardware connections to the ATS lamp.

REMOTE TRANSFER LOGIC

To transfer from operator automatic to a remote mode, the operatorsimply presses the appropriate pushbutton on the Operator's Panel. Then,assuming all permissive conditions as described elsewhere in thiswriteup are satisfied, the new mode will be selected with a bumplesstransfer in which the turbine valves remain at the existing position. Inaddition, a lamp behind the pushbutton selected will be turned on andthe lamp for the previous mode will be turned off. Conversely, in orderto return from any remote mode to operator automatic, the operatorsimply presses the OPER AUTO pushbutton. The remote transfer logicprogram detects operating mode changes and updates the panel lampsaccording.

As shown in FIG. 30, the temporary logical variable (T3), which has beenupdated in earlier portions of the logic program, is checked todetermine if any remote state has been selected. If so, the operatordemand (ODMD) is set equal to the current reference (REFDMD), andlogical flags are set to run the LOGIC task again to set the appropriateconditions in the DEH system. Then the status of the operator automaticlamp (OALITE) is determined since a remote control mode selection mustresult in turning off this lamp. Finally, a call to the LCCO subroutineis made to place this lamp in the proper state.

PANEL TASK

FIG. 32 shows a block diagram of the major functions performed by thePANEL task. These include executing each of the button group functionsdiscussed above, as well as additional decisions, checks, andbookkeeping necessary to properly perform the action requested by theoperator.

BUTTON DECODE

The BUTTON DECODE program examines the button identification (IPB)provided by the PANEL INTERRUPT program, and transfers to the properlocation in the PANEL task to carry out the action required by thisbutton. The program also does some bookkeeping checks necessary to keepthe panel lamps in the correct state. A total of 54 buttons can bedecoded in the current version of the DEH PANEL task.

The identification of the last button (IPBX), which had been pressed andwhich has associated with it a visual display mode lamp, is stored in atemporary integer location (JJ) for later use in turning off the lastlamp. Then the current button identification (IPB) is checked todetermine if it represents the ENTER pushbutton; if so, a speciallogical variable ENTERPB is reset for later use should the ENTER buttonbe pressed two or more consecutive times. This has been found to be arather common operator error and is flashed as an invalid request. Theprogram then simply executes a FORTRAN computed GO TO statement andtransfers to the appropriate portion of the PANEL task.

CONTROL SYSTEM SWITCHING

There are six buttons on the Operator's Panel which may switch controlstates of the DEH system. A brief description of each follows:

1. TRANSFER TV/GV -- This button initiates a transfer from throttlevalve to governor valve control during wide-range speed operation. Thepushbutton has a split lens. When control is on the throttle valves, theupper half of the lens is backlighted. When the button is pressed, totransfer control, the entire lens is backlighted. At the completion ofthe transfer, only the bottom half of the lens remains on. Once the DEHsystem is on governor control, it stays in this mode until the turbineis tripped and relatched. At this time, it is again in throttle valvecontrol.

2. IMPULSE PRESSURE FEEDBACK IN/OUT -- This is a push-push button withsplit lens. It places the impulse pressure feedback loop in or out ofservice, with appropriate backlighting of the button lens.

3. MEGAWATT FEEDBACK IN/OUT -- This is a push-push button with splitlens. It places the megawatt feedback loop in or out of service, withappropriate backlighting of the button lens.

4. SPEED FEEDBACK IN/OUT -- This split lens button places the speedfeedback loop in service in the DEH system. Normally the speed loop isalways in service; however, when the DEH CONTROL task detects a speedchannel failure condition in which all speed input signals areunreliable, the speed feedback loop is disabled and the speed channelmonitor lamps turned on. When the speed inputs become reliable, themonitor lamps are turned off, thus indicating to the operator that hemay place the speed feedback loop back in service. As long as the speedsignals are reliable, the operator cannot take the speed loop out ofservice.

5. THROTTLE PRESSURE CONTROL IN/OUT -- This is a push-push button withsplit lens which places the throttle pressure controller in or out ofservice, with appropriate backlighting of the lens.

6. CONTROLLER RESET -- The button restores the DEH system to an activeoperating state after the computer has been stopped due to a powerfailure or hardware/software maintenance.

The logical variable TRPB is set when the TRANSFER Tv/GV button ispressed. The impulse pressure, megawatt, and throttle pressure logicalstates (IPIPB, MWIPB AND TRCPB respectively) are set to the logicalinverse of their previous state when the corresponding buttons arepressed. This is the mechanism which provides the push-push nature ofthese buttons. The logical variable SPIPB is set when the speed feedbackbutton is pressed. Finally, each of these buttons initiate a bid for theLOGIC task by setting the RUNLOGIC variable prior to exit from the PANELtask.

The CONTROLLER RESET button is handled somewhat differently. The stateCRESETPB is set by the STOP/INITIALIZE task, which does cleanup andinitialization after a computer stop condition. Then CRESETPB ischecked; if it is not set, the computer has been running, and thus thebutton pressed is ignored. If CRESETPB is set, this means the computerhad been stopped; CRESETPB is reset and the lamp behind the button isturned off. In addition, the PANEL task effectively presses the speedfeedback button by setting the logical state SPIPB. This is done so thatthe DEH system restarts after a power failure or other computer stopcondition with the speed feedback loop in service. The LOGIC task isrequested to run by setting the RUNLOGIC state. The REFERENCE displaybutton is also effectively pressed so that the display windows alwaysstart out in the same mode after a stop condition on the computer.

DISPLAY/CHANGE DEH SYSTEM PARAMETERS

Eight buttons allow the operator to display or change various DEH systemparameters. Six of these buttons are dedicated to the display or changeof a single important parameter for each button. The remaining twobuttons provide the ability to display or change a group of DEH systemvariables from each button. In addition, two special buttons (GO andHOLD) are intimately associated with one of the dedicated display/changebuttons, and thus are also included in this discussion.

Before listing each of these buttons, a brief description of the displaywindow mechanism is given. The DEH Operator B Panel contains two digitaldisplays which are provided with five windows each. The left display,labeled REFERENCE, has two major functions. It either presents numericalinformation which currently exists in computer memory for the sixdedicated buttons mentioned above, or it accepts address inputs from thekeyboard for the two buttons assigned to display or change groups of DEHsystem variables. The right display, labeled DEMAND, also has two majorfunctions. It either accepts keyboard inputs in preparation for changingany of the currently existing numerical information in computer memoryfor the six dedicated buttons mentioned above, or it presents currentlyexisting information in computer memory for the two buttons assigned todisplay or change groups of DEH system variables.

Of the five windows in each digital display, the left-most is reservedfor mnemonic characters. These characters combine to form a shortmessage identifying the numerical quantity in the remaining fourwindows. The following table lists the 11 available messages and anexplanation of each. The four right windows in each display provide thenumerical digits 0 through 9 and a decimal point where appropriate.

    MNEMONIC CHARACTER DEFINITION                                                 Message     Explanation                                                       ______________________________________                                        MW          Megawatt Symbol for Load Control                                  SPEED       Speed Symbol for Speed Control                                    % VALVE POSITION                                                                          Percent Valve Position for Valve Status                           RPM/MIN     Acceleration Rate                                                 MW/MIN      Load Rate                                                         SYS PAR     General DEH System Parameter                                      IMP PRESS % Impulse Pressure in Percent For Load                                          Control                                                           PRESS       General Pressure Variable                                         TEMP        General Temperature Variable                                      VALVE NO.   Valve Identification for Valve Status                                         Algebraic Negative Quantity                                       ______________________________________                                    

A brief description of the eight buttons associated with display/changeas well as the GO and HOLD buttons, follows:

1. REFERENCE -- This button initiates a display or change of the DEHreference and demand for speed or load operation. When the turbine is onoperator automatic control, new demand values may be entered from thekeyboard. However, when the turbine is in a remote operating mode suchas automatic synchronizer, dispatch or ACCELERATION program, the demandcannot be changed from the keyboard. Any attempt to do so is flashed asan invalid request.

2. ACCELERATION RATE -- This button initiates a display or change of theacceleration rate used on wide-range speed operation. When the turbineis on operator automatic control, this value is entered by the operator,and may be changed from the keyboard. However, when the turbine is beingaccelerated by an AUTOMATIC STARTUP program, the displayed value is therate selected by this program and cannot be changed from the keyboard.Any attempt to do so is flashed as an invalid request.

3. LOAD RATE -- This button initiates a display or change of the loadrate used on operator automatic control. This value may be displayed orchanged at any time.

4. LOW LIMIT -- This button is an optional feature which initiates adisplay or change of the low load limit used on all automatic loadcontrol modes. This value may be displayed or changed at any time.

5. HIGH LIMIT -- This button is an optional feature which initiates adisplay or change of the high load limit used on all automatic loadcontrol modes. This value may be changed at any time.

Each of these buttons have high or low limits, whichever is appropriate,associated with them when changes are to be made in the values discussedabove. Violation of these limits from a keyboard entry is flashed as aninvalid request and the entry is ignored. More details of these limitsare discussed in a later section where the KEYBOARD program isdescribed.

6. VALVE POSITION LIMIT -- This button initiates a display of thegovernor valve position limit and the quantity being limited. Change oradjustment of the valve position limit is accomplished by raise/lowerbuttons (described in a later section where the valve buttons arediscussed). Any attempt to enter values from the keyboard in thisdisplay mode is flashed as an invalid request.

7. VALVE STATUS -- This button initiates a display of the status(position) of the turbine throttle and governor valves. Thus, thisbutton is associated with a group of DEH system variables. A descriptionof the steps necessary to carry out this display function is given inlater paragraphs (where the valve buttons are discussed).

8. TURBINE PROGRAM DISPLAY -- This button initiates a display or changeof any DEH system parameter not otherwise addressable with one of theunique buttons described above. These variables include pressures,temperatures, control system tuning constants, and calculated quantitiesin all parts of the DEH system. A dictionary is provided so that theaddress of such quantities may be entered from the keyboard. Furtherdiscussion of these points is given in later paragraphs where thekeyboard is described.

9. GO -- This button initiates a special DEH CONTROL program to adjustthe turbine reference. The program ultimately positions the valves onoperator automatic control. The reference then moves at the appropriateload or acceleration rate until the reference and demand are equal. Theupdated reference value is continually displayed in the REFERENCEwindows so that the operator may observe it changing to meet the demand,which is displayed in the DEMAND windows.

10. HOLD -- This button interrupts the reference adjustment processdescribed above, and holds the reference at the value existing at themoment the HO-LD button is pressed. In order to continue the adjustmentprocess on the reference, the operator must press the GO button.

A brief description of the steps necessary to display or change any ofthe first six variables discussed above follows; description of cases 7and 8 are withheld until a later section. When the operator wishes todisplay or change any of the DEH dedicated system parameters, he mustexecute a sequence of steps which result in the desired action. Thesteps are listed as follows:

1. The operator presses the appropriate button; the DEH programs displaythe current value of the parameter in the reference windows while thedemand windows are cleared to allow for possible keyboard entry.

2. If the operator wishes only to observe the parameter value, then hedoes nothing else. The value remains in the reference windows until somenew button is pressed.

3. If the operator wishes to change the parameter, he types in on thekeyboard the new value which he desires. This is displayed in the DEMANDwindows, but will not yet be entered into the DEH programs.

4. If the operator is satisfied with the new value as it appears in thedemand windows, he may enter the new quantity into the DEH operatingsystem by pressing the ENTER button. The ENTER button is described inmore detail in a later section on the keyboard.

5. If for any reason the operator is not satisfied with the value as itappears in the demand windows, he may press the CANCEL button. TheCANCEL button will be described in more detail in a later section on thekeyboard. This removes the number from the DEMAND windows and allows theoperator to begin a new sequence for the parameter.

6. Assuming that the operator is satisfied with the number and that hepresses the ENTER button, the new value of the parameter appears in theREFERENCE window and the DEMAND window is cleared. This is anacknowledgement that the DEH programs have accepted the number and areusing the new value from that point on.

7. If for any reason the numerical value entered into the DEH systemviolates preprogrammed conditions (such as high limits less than lowlimits), the entire operation is aborted and the INVALID REQUEST lamp isflashed.

The above description of data manipulation is modified somewhat when theoperator wishes to display or change the turbine reference and demand.Both of these quantities are displayed when the reference button ispressed. During wide-range speed control, the left REFERENCE displaycontains the turbine speed reference value, while the right DEMANDdisplay contains the turbine speed demand. During load control theREFERENCE display contains the turbine load reference while the demanddisplay contains the turbine load demand.

Since the reference and demand control the turbine valves directly, itis essential that the operator have a unique handle on these quantitiesso that he may start or stop reference changes quickly and easily. Thisis accomplished by use of the GO and HOLD buttons in conjunction withthe reference button. The GO and HOLD buttons control two referencestates in the DEH system, which indicate whether the reference anddemand are equal or unequal. When these quantities are equal, both theGO and HOLD backlights are off. When these quantities are unequal,either the GO or the HOLD lamp is on. If the GO light is turned on, thereference is changing to meet the demand value at the selected rate.Should the operator wish to stop the reference adjustment process, hesimply presses the HOLD button. The HOLD button then backlights andholds the reference at its current value. When the operator wishes tostart the reference moving again, he must press the GO button, whichthen backlights and enables the reference to adjust to the proper value.

The sequence of steps for displaying or changing the reference follows:

1. The operator presses the reference button. The DEH programs displaythe current value of reference in the left windows and the current valueof demand in the right windows.

2. If the operator wishes to change the demand, he types the new valueon the keyboard. This is displayed in the DEMAND windows, but is not yetentered into the DEH programs.

3. If the operator is satisfied with the new value, he presses the ENTERbutton. This places the new demand value in the DEH programs and turnsthe HOLD lamp, assuming that the new demand satisfies certain limitchecks to be described shortly. If these conditions are not met, theINVALID REQUEST lamp is flashed, the new value is ignored, and theoriginal value is returned to the DEMAND windows.

4. If the operator is not satisfied with the new value (set in Step 3),he simply presses the CANCEL button. The DEH programs then ignore thisvalue and return the original value to the DEMAND windows.

5. If a new demand is finally entered and the HOLD lamp comes on, theoperator may start the reference adjusting to this new demand bypressing the GO button. The HOLD lamp is turned off, the GO lamp isturned on, and the reference begins to move at the selected rate towardthe demand.

6. At any time, the operator may inhibit the reference adjustment bypressing the HOLD button. He may then restart the reference adjustmentby pressing the GO button.

7. When the reference finally equals the demand both the GO and HOLDlamps will be turned off.

Each of the eight display buttons set the integer pointer (IPBX) to itsassigned value and the appropriate panel lamps are turned off and on.IPBX is then checked by the VISUAL DISPLAY task, which selects thenumerical values from computer memory and displays then in the windows.

The TURBINE PROGRAM DISPLAY button also resets a few logical states inpreparation for keyboard entries. These are discussed in laterparagraphs on the keyboard description. The remote control modes AS, ADSand ATS for the Automatic Synchronizer, Dispatch System and TURBINESTARTUP program are checked, along with the manual control state (TM) ifthe maintenance test switch (OPRT) is not set. All of these modesexclude the possibility of the GO and HOLD buttons being active, sothese buttons are ignored in these states and the PANEL program simplyexits. However on operator automatic control, the HOLD button state(HOLDPB) is set, or the GO button state (GOPB) is set. In the lattercase, HOLDPB is also reset. The LOGIC task is requested to run bysetting the RUNLOGIC variable, and the program then exits.

OPERATING MODE SELECTION

There are five buttons which may be used to select the turbine operatingmode. When any of these are pressed, they initiate major operatingchanges in the DEH Control System, assuming the proper conditions existfor the mode selected. A brief description of these buttons follows:

1. OPERATOR AUTOMATIC (OPER AUTO) -- This button places the turbine inautomatic control with the operator providing all demand, rate, and setpoint information from the keyboard. If the turbine had been previouslyin manual control, the OPER AUTO lamp must be flashing to indicate thatthe DEH system is ready to accept automatic control; otherwise pressingthe OPER AUTO button is ignored. If the turbine had been in one of theremote control modes listed below, then pressing the OPER AUTO buttonrejects the remote and returns automatic control to the operator.

2. AUXILIARY SYNCHRONIZER (AUTO SYNC) -- This button allows automaticsynchronizing equipment to synchronize the turbine generator with thepower system by indexing the speed demand and reference with raise/lowerpulses, in the form of contact inputs.

3. AUTOMATIC DISPATCHING SYSTEM (ADS) -- This button allows automaticdispatching equipment to operate the turbine generator by setting theload demand and reference. A number of dispatching options areavailable, including raise/lower pulses, raise/lower pulse-widthmodulation, and analog input values to set the reference.

4. AUTOMATIC TURBINE STARTUP (TURBINE AUTO START) -- This button allowsa special computer program to automatically start up and accelerate theturbine during wide-range speed control. The program may reside in theDEH computer or it may exist in another computer in the plant or at aremote location.

5. COMPUTER DATA LINK (COMP DATA LINK) -- This optional button allowsanother computer, either in the plant or at a remote location, toprovide all demand, rate, and set point information to the DEH system.

The OPER AUTO button resets the remote mode button states (ASPB, ADSPBand AUTOSTAR) for Automatic Synchronizer, the Automatic Dispatch System,and the AUTOMATIC TURBINE STARTUP program, respectively. Since theoperator automatic state (OA) is merely the logical inverse of theturbine manual state (TM), the PANEL task cannot actually set OA, butcan only request the LOGIC task to run, by setting the RUNLOGICvariable. The LOGIC program then determines whether or not operatorautomatic is accepted by the manual backup system.

The remote buttons set their corresponding pushbutton states after whichRUNLOGIC is set. As in the case of operator automatic, the LOGIC taskthen determines if the requested mode will be accepted.

The data link button is handled somewhat differently; this is apush-push button whose state (DLINK) is given the logical inverse of itsprevious value at statement 14. The new state is then interrogated inorder to determine whether to turn the button backlight on or off, afterwhich the program exits.

AUTOMATIC TURBINE STARTUP

Five buttons are associated with the automatic turbine startup featureof the DEH system. A brief description of these buttons follows:

1. AUTOMATIC TURBINE STARTUP (TURBINE AUTO START) -- This button allowsa special computer program to automatically start up and accelerate theturbine during wide-range speed control.

2. TURBINE SUPERVISION OFF -- This is a push-push button which controlsthe printout of messages from the turbine supervisory programs.Normally, the messages are always printed; the operator may suppressprinting by pressing this button, which then backlights. Should themessages be desired later, then the button may be pressed again; thelamp is turned off and the supervisory messages are printed on thetypewriter.

3. OVERRIDE ALARM -- This button overrides certain alarm stops which theAUTOMATIC TURBINE STARTUP program may detect. When this happens, theprogram waits for operator action before proceeding with theacceleration. If the operator decides to continue the startup, hepresses the OVERRIDE ALARM button.

4. OVERRIDE SENSOR HOLD -- This button overrides certain analog inputsensor stops, which the AUTOMATIC TURBINE STARTUP program may detect.When this happens, the program waits for operator action beforeproceeding with the acceleration. If the operator decides to continuethe startup, he presses this button.

5. RETURN SENSOR TO SCAN -- This button returns certain analog inputs toscan after their sensor has been repaired. Should a sensor fail, theAUTOMATIC TURBINE STARTUP removes the corresponding input from scan;when the sensor is detected valid again, this button is backlighted tonotify the operator. He then presses the button to return the input toits normal scan.

MANUAL BUTTONS

Six buttons on the Operator's Panel are associated with manual operationof the turbine. Even though the DEH PANEL program does not interfacedirectly with these buttons, a brief description of their funcion isgiven for completeness. In general, these buttons allow the operator tocontrol the position of the turbine throttle and governor valvesdirectly from the panel.

1. TURBINE MANUAL -- This button places the turbine under manual controlof the operator, with the transition from automatic being achievedessentially bumplessly.

2. TV LOWER -- This button lowers, or decreases, the throttle valves ata fixed rate as long as the button is held down.

3. TV RAISE -- This button raises, or increases, the throttle valves ata fixed rate as long as the button is held down.

4. GV LOWER -- This button lowers, or decreases, the governor valves ata fixed rate as long as the button is held down.

5. GV RAISE -- This button raises, or increases, the governor valves ata fixed rate as long as the button is held down.

6. FAST ACTION -- This button opens or closes the throttle and governorvalves, at a fast rate, in manual control. The FAST ACTION button mustbe held down at the same time as any of the TV or GV RAISE/LOWER buttonsdescribed above to achieve the fast action effect.

KEYBOARD ACTIVITY

There are fourteen buttons associated with keyboard activity on the DEHOperator's Panel. Of this total, eleven are numerical keys; theseinclude the integers 0 through 9 and a decimal point. Three additionalbuttons are available for use with the keyboard to aid in data displayor change. A brief description of these buttons follows:

1. NUMERICAL BUTTONS 0 THROUGH 9 -- When the operator keys in numbers ofthese buttons, the correspoding values are displayed in the reference ordemand windows, whichever are appropriate, for the function beingperformed. The values move from right to left in the windows as new keysare pressed, and both leading and trailing zeros are always displayed.If more than four numerical keys are pressed, the left-most value in thewindows is lost as the new value is entered in the right-most window,and the remaining values shift left one position.

2. DECIMAL POINT BUTTON -- When the decimal point key is pressed, thePANEL program retains this information but does not yet display it. Whenthe next numerical key is pressed, both the value and the decimal pointappear in the right-most window. The decimal point is positioned in thelower left-hand corner of the window position. Should additionalnumerical keys be pressed, the decimal point moves one position to theleft with the number with which it was originally entered. Should thedecimal point be shifted out of the left-most window it is lost, and anew point may be entered.

3. ENTER -- When this button is pressed, the PANEL program enters thevalue residing in the reference or demand windows, whichever isappropriate, into core memory and performs the correct action requestedby the keyboard activity. This action may consist of visual display,parameter change, or intermediate steps in a sequence of operations asdescribed in preceding sections.

4. CANCEL -- When this button is pressed, the PANEL program clears boththe reference and demand windows, deletes any intermediate values incomputer memory, and aborts the entire sequence of operations which wascanceled. The operator may then begin a new sequence of steps.

5. CHANGE -- This button indicates a sequence of operations necessary toalter numerical values residing in the DEH system memory. The stepsnecessary to change parameters are described earlier.

The decimal point key and keys 0-9 are serviced to check the validity ofthe requested entry and to set the entry if it is valid. Among otherchecks, a check is made on the integer IPBX, which represents the visualdisplay and change button which has been previously pressed. If thisvalue equals 2, thus indicating the acceleration rate button has beenpressed, and the Automatic Turbine Startup mode (ATS) is in control, allkeyboard buttons are invalid. During the ATS mode the acceleration rateis controlled by the startup program, and thus may be visually displayedbut cannot be changed from the keyboard.

Should the ATS state be satisfied, the pointer IPBX is checked todetermine if it is equal to 6; if so, the keyboard entry is flashed asinvalid because this represents the valve position limit display mode,which cannot use the keyboard. If this situation is all right, the valvetest button state (VTESTPB) is checked; should VTESTPB be set and thevalve being tested NVTEST is non-zero, the keyboard entry is invalid.This is because NVTEST indicates that some valve has already beenselected for test, thus implying that no further keyboard activity isnecessary.

Finally, some special tests are made if IPBX equals 1; this means thereference display mode has been selected. If this is the case, allremote control modes such as Automatic Synchronizer (AS), AutomaticDispatch System (ADS), and Automatic Turbine Startup (ATS), imply thatthe keyboard cannot be used during reference display. Thus these resultin the INVALID REQUEST lamp being flashed. In addition, should theturbine be on manual control (TM) or unlatched (NOT ASL), and not in themaintenance test mode (OPRT), then keyboard activity is also invalidduring reference display. All of these cases are invalid for keyboardentry because the turbine demand and reference are set by the remotemode or the manual tracking system. The only time that the operator mayuse the keyboard in the reference display mode is during operatorautomatic control or during the maintenance test condition in which theDEH system is being used as a simulator and trainer.

Should all of these tests be passed properly, the logical state KEYENTRYis set and the numerical value in location KEY is checked. This is thekeyboard button which has just been pressed, and must lie between 0 and9 inclusive; otherwise, the entry is flashed as invalid. For a validvalue of KEY, the program then places the new number in its properposition in the integer array (IW). This array has a place for each ofthe four window positions of the visual display and, as keyboard buttonsare pressed, the entries move down one position in IW and the latest keyis entered in the top position. The pointer ID maintains the properposition for each new key. Thus, if ID equals 0, this means there are noentries in the array IW. The value KEY is thus placed in the firstposition of IW. However, if ID is not zero, then a FORTRAN DO loop isexecuted to move the entries in IW down one position prior to enteringthe new value of key in the first position at statement 414. Then thevalue of the pointer ID is checked again; if it is less than 3, it isincremented by 1. If it is equal to 3, it retains that value. This isthe mechanism used to accept more than four keyboard values with onlythe last four key entries being retained.

CONTROL TASK Speed Selection Function

An additional task which the speed selection function must accomplish isthe bumpless transfer mechanisms necessary when the speed input signalsare switched, and when all speed inputs fail. These bumpless transfersare incorporated only on load control, since speed switching then can besignificant in affecting governor position and thus turbine load. Duringspeed control, no noticeable effect of speed signal switching may beexpected.

Consider first the case when the speed signal is to be switched from thedigital to the analog channel, or from the analog to the digitalchannel. The portion of the Load Control System which will be affectedby such a change includes essentially the speed feedback loop output (X,considered simply as a single block since the details are not importantin this context), the turbine load reference (REFDMD), and the turbinespeed modified load reference (REF1).

When the speed signal is switched, the factor X changes, in general, soit is necessary to change the reference (REFDMD) to avoid a bump in REF1and ultimately in the valves. Suppose that the system has been using oneof the two speed inputs (it is immaterial which one), and thus had beenyielding a speed feedback factor (X₁). Then the value of REF1 is givenby:

    REF1.sub.1 = REFDMD.sub.1 + X.sub.1                        (35)

Now the system switches to the other input and yields a speed feedbackfactor (X₂). The corresponding value for REF1 is given in:

    REF1.sub.2 = REFDMD.sub.2 + X.sub.2                        (36)

To yield a bumpless transfer, it is necessary to hold the value of REF1constant, as indicated in the following expression:

    REF1.sub.2 = REF1.sub.1 Substituting Equations (35) and (36) into (37) and solving for the new value of REFDMD gives the proper condition for a bumpless transfer, as shown below:

    REFDMD.sub.2 = REFDMD.sub.1 + X.sub.1 - X.sub.2            (38)

Thus when the speed signal is switched, the speed selection functionrecomputes the new value of turbine reference according to Equation (38)and achieves the required bumpless transfer.

Consider next the situation in which both the digital and the analogsignals fail, thus requiring the speed feedback loop to be disabled andtaken out of service. Again this must be accomplished bumplessly so thatthe governor valves, and thus turbine load, do not change significantly.The value of the speed compensated reference when the speed loop (SPI)is in service is given by:

    REF1.sub.in = REFDMD.sub.in + X                            (39)

When the loop is taken out of service due to speed channel failure, thevalue of REF1 is computed from:

    REF1.sub.out = REFDMD.sub.out                              (40)

To yield a bumpless transfer, it is necessary to hold the value of REF1constant as follows:

    REF1.sub.out = REF1.sub.in                                 (41)

Substituting Equations (39) and (40) into (41) and solving for the newvalue of REFDMD gives the proper conditions to maintain a bumplesstransfer, as shown below:

    REFDMD.sub.out = REFDMD.sub.in + X                         (42)

Thus, to satisfy the conditions for bumpless transfer with respect tothe speed loop, the speed selection function must reset the reference asgiven in Equation (42) to maintain constant valve position and thusconstant load during this interval. Brief consideration will now bedirected to the two out of three logical error detection scheme used bythe speed selection function. It must be realized first that the threespeed signals will rarely, if ever, be exactly equal; thus, it isnecessary to compare these signals with each other and check for asignificant difference. The value of the allowable difference given byWSERROR and is a keyboard entered constant; should any two speeds differin magnitude greater than WSERROR, then one or both of the speeds arefaulty. The allowable speed error (WSERROR) is usually set about 100rpm.

The speed selection process compares the three speeds and bases itslogical conclusions on the results of this test. Since there are threedifferences (between the digital and the analog, the digital and thesupervisory, and the analog and the supervisory), which may or may notbe greater than WSERROR, then there are eight possible combinationswhich must be examined. Table 1 lists these combinations, the decisionas to which speed to be used, and a comment on each situation. Thecolumn titles in Table 1 indicate "approximately equal", which meansthat the various speeds agree within WSERROR rpm. The letter Y in thetable means YES they do agree, while the letter N means NO they do notagree.

The speed selection function simply compares the speed differences whichexist every 1 sec (the sampling interval for the CONTROL task) and findsthe corresponding entry in Table 1. Logical conditions are then set tocarry out the appropriate action as indicated by the comments in Table1, to assure proper control by the remaining parts of the DEH system.

SELECT OPERATING MODE FUNCTION

The SELECT OPERATING MODE program must distinguish between speed andload control by examining the state of the main generator circuitbreaker. For wide-range speed control, the program flow chart is shownin FIG. 37A. The automatic synchronizer state (AS) is firstinterrogated; if it is the operating mode, the auto sync increase anddecrease states (ASINC and ASDEC) are examined. These states areflip-flops which are controlled by the LOGIC task when the auto syncraise or lower contact inputs are set. The program carefully checks tosee if both the increase and decrease states are set; if so, no actionis taken. Otherwise a temporary location (TEMP) is set to +1 rpm or -1rpm for each pass through the program during which the appropriatecontact input is set. The turbine speed reference and demand are thenincremented properly, the ASINC and ASDEC states are reset for the nexttime, and the program passes to the next stage of the CONTROL task.

If the automatic synchronizer is not the operating mode, then theAutomatic Turbine Startup (ATS) state is interrogated at statement 4000(FIG. 37A. If it is the operating mode, as determined by the LOGIC task,the turbine speed demand and rate are selected from this program viacomputer locations TASDMD and TASRATE. The rate is then checked againstan absolute high limit (OARATMAX), which is a keyboard entered constantusually set at 800 rpm after which the program passes on to the nextstage of the CONTROL task.

If the AUTOMATIC TURBINE STARTUP program is not the operating mode, theOperator Automatic (OA) state, and the Maintenance Test (OPRT) state areinterrogated at statement 6000 (FIG. 37A). If either of these states areset, the turbine speed demand and rate are selected from the keyboardand the program proceeds to the next stage of the CONTROL task. Notethat on Operator Automatic the keyboard values control the turbine,while in Maintenance Test the keyboard values simulate a turbine.

If neither Operator Automatic nor Maintenance Test is the operatingmode, then the turbine is in Manual control and the SELECT OPERATINGMODE program goes into the manual tracking mode at statement 7000. Ifthe contact input (THI) is set, this means the throttle valves are wideopen and the turbine is in speed governor control. Then the errorbetween manual and computer governor valve outputs (IGVMAN and IGVAO) ismultiplied by a gain factor (GR10) and saved in a temporary location. Ifthe contact input (THI) is not set, then the turbine is in speedthrottle control and the error between manual and computer throttlevalve outputs (ITVMAN and ITVAO) is multiplied by a gain factor (GR5)and saved in a temporary location.

In either case, assuming the speed loop (SPI) is in service, the valveoutput error is checked against a speed tracking deadband (DBTRKS, whichis a keyboard entered constant usually set at 1 percent) and thereference is checked against actual speed (WS) through a referencetracking deadband (DBTRKREF, which is also a keyboard entered constantusually set at 50 rpm). If both conditions are met, the READY state isset to indicate the DEH system is ready to assume automatic control. TheREADY state is detected by the FLASH task, which then flashes the OPERAUTO light to let the operator known that he may transfer to automaticcontrol.

Finally, the gained valve position error in the temporary location(TEMP) is uused to increment the reference (REFDMD), which is thenchecked against an absolute high speed limit (HLS). This is a keyboardentered constant which is normally set at 4200 rpm. The program thentransfers to statement 15500 for some final bookkeeping checks.

When the SELECT OPERATING MODE program determines that the maingenerator circuit breaker is closed, thus indicating the turbine is onload control, transfer is made to statement 10000 which is shown in FIG.37B. The Throttle Pressure Control (TPC) state is interrogated; if it isin service, then the actual throttle pressure (PO) is compared against aset point (POSP), which is a keyboard entered constant usually set atabout 1600 psia. If the throttle pressure (PO) is above the set point(POSP), no further action is taken. But if PO is below POSP, then thegovernor valve position (GVSP) as called for by the computer is checkedagainst a minimum governor valve set point (GVSPMIN). This is a keyboardentered constant usually set at about 25 percent. If GVSP is less thanGVSPMIN, no further action is taken; but if GVSP is greater thanGVSPMIN, then the throttle pressure limiting state (TPLIM) is set andthe reference load rate is set to runback the reference at the rateTPCRATE, which is a keyboard entered constant usually set at 200 percentper minute. The program then transfers to statement 11500 for furtherbookkeeping computation.

If no throttle pressure contingency exists, the RUNBACK contact input(RB) is interrogated; if it is set, the load reference is runback at therate (RBRATE, which is a keyboard entered constant set at about 100percent per minute. Then at statement 11500 some bookkeeping details aretaken care of. Thus if the Automatic Dispatch System (ADS) state hasbeen in control when either a throttle pressure limit or runbackcondition occurred, this mode is rejected by resetting the automaticdispatch system pushbutton state (ADSPB) and setting the RUNLOGIC flag.Within 1/10 sec the AUX SYNC task bids the LOGIC task, which thenrealigns all states to the correct position. A second bookkeeping checkis made at statement 11700 where the HOLD state is checked. If HOLD isreset, then it is set so that the operator has an indication of why thereference has been runback.

If no runback contingency exists, then the Automatic Dispatch System(ADS) state is interrogated at statement 1200. If it is the operatingmode, the ADS increase and decrease states (ADSINC and ADSDEC) areexamined. These are flip-flops which are controlled by the LOGIC taskwhen the ADS increase and decrease contact inputs are set. The programcarefully checks to see if both the increase and decrease contacts areset; if so no action is taken. Otherwise a temporary location (TEMP) isset to the ADS raise or lower pulse count (IADSUP or IADSDOWN). The AUXSYNC task keeps track of these pulse counts according to the conditionsset up by the LOGIC task. However, a maximum ADS pulse-width is imposedon both the raise and lower pulses in the SELECT OPERATING MODE programby comparing their counts (IADSUP and IADSDOWN) with a limit (ADSMAXT),which is a keyboard entered constant usually set to 10 counts of 1/10sec each (thus yielding a maximum pulse-width of 1 sec). After thepulse-width limiting action, at statement 12400 the turbine loadreference and demand are incremented by an amount proportional to thepulse-width; the proportionality factor (ADSRATE) is a keyboard enteredconstant usually set somewhere between 1 and 10 MW per sec ofpulse-width. Finally, at statement 12600, various ADS counters andstates are reset prior to moving on to the next stage of the CONTROLtask.

If the ADS state is not set, then the select operating mode programchecks the Operator Automatic (OA) state and the Maintenance Test (OPRT)state at statement 14000. If either of these states are set, then theturbine demand and rate are accepted from the keyboard and the programproceeds to the next stage of the CONTROL task. Note that in OperatorAutomatic the keyboard values control the turbine, while in MaintenanceTest the keyboard values simulate a turbine.

If neither Operator Automatic nor Maintenance Test is the operatingmode, then the turbine is in Manual control and the SELECT OPERATINGMODE program goes into the Manual Load Tracking mode at statement 1500.The error between the manual and computer governor valve outputs (IGVMANand IGVAO) is stored in a temporary location (TEMP) and compared againsta load tracking deadband (DBTRKL), which is a keyboard entered constantusually set at about 1 percent. If the outputs agree within DBTRKL, thenthe READY state is set to indicate the DEH system is ready to assumeautomatic control. The READY state is detected by the FLASH task, whichthen flashes the OPER AUTO light to let the operator know that he maytransfer to automatic control.

The valve output error is then gain multiplied by GR9 and added to thecurrent reference (REFDMD), which is high-limit-checked against MWMAX, akeyboard entered constant usually set to about 120 percent of ratedmegawatts. REFDMD is also low-limit-checked against zero, thus assuringthat the tracking scheme will not windup in either direction. Finally, alast check is made to determine if a voltage exists on the test analogoutput lines; if so, the READY state is reset so that transfer toautomatic control is inhibited until this voltage is removed. This maybe done by pressing the OPEN valve test pushbutton until the lightsbehind the OPEN and CLOSE pushbutton go out.

SPEED/LOAD REFERENCE FUNCTION

The GO state is checked; if GO is off, the HOLD state is checked. IfHOLD is on and the demand and reference value (REFDMD) are equal, thenthe logical states (GOHOLDOF and RUNLOGIC) are set. This results in theLOGIC task being bid within 1/10 sec by the AUX SYNC task, whichrecognizes the RUNLOGIC state. The LOGIC task then turns off the HOLDflip-flop and lamp as requested by the GOHOLDOF state.

If the GO state is set back however, then this is the signal to allowthe reference to move toward the demand. The magnitude of the differencebetween the reference and the demand is computed and stored in atemporary location. Then the magnitude of the incremental step sizetaken each second by the selected rate, as discussed above, is saved inanother temporary location. These two temporary quantities are thencompared and if the demand/reference difference in TEMP is greater thanthe incremental step size in TEMP1, this means the reference mustcontinue to move closer to the demand. However, the governor valveposition limiting state (VPLIM) is checked; if it is set and the demandis above the reference, then no movement is allowed in the reference.This is because the valve position limit function is operating andrefuses to allow any increase in reference because this will attempt toincrease the governor valve position beyond the limit.

If there is no valve position limiting action, then the reference isincremented by the incremental rate step size and the program transfersfor final exit.

Eventually the reference will approach within the allotted boundary ofthe demand. Then the reference program immediately sets the referenceequal to the demand. Finally, the state of the breaker (BR) isinterrogated; if it is set, the program transfers for the Load ControlSystem computations, while transfer is made for the Speed Control Systemcomputations if the breaker state (BR) is reset.

SPEED CONTROL FUNCTION

To provide the simulation and training feature, FIG. 39 shows anadditional program path which will internally generate a simulated speedsignal (SIMWS) in the Maintenance Test mode of operation. This isaccomplished by feeding back the speed controller output (SPDSP) througha first order lag transfer function which approximates the turbineinertia response. This simulated speed then replaces the actual speed indeveloping a speed error during the Simulation/Training mode ofoperation.

All speed control system parameters, such as gains, reset times andlimits, are keyboard entered constants which are available for tuning oradjustment during the Maintenance Test mode. These changes requiretransfer of the turbine control to manual operation.

Logical checks are made to determine whether the speed computationsshould be evaluated. Thus, if the speed inputs failed and areunreliable, then the speed loop (SPI) is taken out of service, and thereis no speed information by which to control the turbine. In addition, ifthe overspeed speed protection circuit in the Analog Backup System isoperating, as indicated by the contact input (OPCOP), this closes thegovernor valve and thus overrides the DEH Speed Control System;consequently in this case, no speed control computations are performed.

Assuming that neither of these situations exist, the speed error iscalculated. If the system is in the Simulation/Training mode, this erroris the difference between the reference and simulated speed; the speederror is the difference between the reference and actual speed in allother cases. Following this error computation, a decision is made as towhether the turbine is on governor or throttle control. Appropriatecalls are then made to the PRESET subroutine to evaluate theproportional-plus-reset controller action for the throttle or governorvalve. This subroutine takes care of evaluating the controller algorithmand the high/low limit checks to eliminate reset windup.

LOAD CONTROL FUNCTION

As in the Speed Control System, all parameters in the Load ControlSystem are keyboard entered constants, which may be tuned or adjusted inthe Maintenance Test mode. As always, changes of this type requiretransfer to manual control for the adjustment, after which the DEHsystem will track and permit return to automatic control.

To provide the simulation and training feature disclosed previously,FIG. 40 shows additional program paths which internally generatesimulated megawatt and impulse pressure signals (SIMMW and SIMPI) in theMaintenance Test mode of operation. These are accomplished by feedingback the load reference (REF2) and the valve set point (VSP) (throughsoftware) to first order lag transfer functions which approximate thegenerator and turbine responses. These simulated signals then replacethe actual feedbacks in developing megawatt and impulse pressure errorsduring the Simulation/Training mode of operation.

A check is first made (FIG. 41) to determine if a change has occurred inthe throttle pressure limit state (TPLIM); if so the LOGIC task alignsall status variables accordingly. The LOAD CONTROL program next checksthe speed transducer failure state (SPTF). If there is no failure, thespeed feedback loop is evaluated with a call to the SPDLOOP subroutine;if there is a speed transducer failure, the speed feedback loop isbypassed and the speed compensation factor (X) is set to zero. Whicheveris the case, the factor (X) is summed with the turbine load reference(REFDMD) to form the speed compensated load reference (REF1). Alow-limit-check against zero is performed on REF1 to keep it from goingnegative, which is possible should a turbine overspeed condition result.

The LOAD CONTROL program then checks the maintenance test contact input(DPRT), which if set means the DEH system is being used as asimulator/trainer or control system tuning is underway. In either case,simulated megawatt and impulse pressure signals (SIMMW and SIMPI) aregenerated; if the turbine is not in this mode, then the simulatedsignals are set equal to the actual signals.

The state of the megawatt feedback loop (MWI) is checked; if the loop isout of service, the speed/megawatt compensated load reference (REF2) issimply set equal to the speed compensated load reference (REF1). But ifthe megawatt loop is in service, the megawatt error is computed andranged to a per unit value by using the ranging gain (GR2), which isnormally set at rated turbine generator megawatts. Then the PRESETsubroutine is called to evaluate the megawatt proportional-plus-resetcontroller, including high/low limit checking. The result of thiscomputation is the megawatt trim factor (Y), which is then applied tothe speed compensated load reference (REF1) in a product relationship toform the speed/megawatt corrected load reference (REF2).

The speed/megawatt compensated load reference (REF2) is converted to animpulse pressure set point (PISP) by use of ranging gain (GR3). Thestate of the impulse pressure feedback loop (IPI) is then interrogated;if it is out of service the governor valve set point (VSP) is simply setequal to the impulse pressure set point (PISP) in psi. But if theimpulse pressure loop is in service, then the impulse pressure error iscomputed and used as the driving signal for the proportional-plus-resetcontroller, which is evaluated by a call to the PRESET subroutine; thisalso does the high/low limit checking.

Finally, the governor valve set point (VSP) in psi is converted to agovernor valve set point from 0 to 100 percent by use of the ranginggain (GR4), which is normally set at rated impulse pressure. The programthen transfers to the final stages of the CONTROL task which actuallycompute the throttle and governor valve outputs.

THROTTLE VALVE CONTROL FUNCTION

The throttle control state (TC) is interrogated (FIG. 42); if it is set,this means the throttle valves are in positive control, and the programcomputes the throttle valve analog output from the speed controllervalue (SPD) and the keyboard entered ranging constant (GR6). However, ifthe throttle control state (TC) is not set, then the governor controlstate (GC) is checked. If it is not set, this means that the turbine isunlatched and that the throttle valves should be at their minimumposition of completely closed. The program then computes the throttlevalve analog output of zero.

If the governor control state (GC) is set, it is then necessary todetermine if the throttle/governor transfer is complete by checking theTRCOM state. If TRCOM is not set, this means the transfer is still inprogress; an additional check is made to determine if the governorvalves have closed as indicated by GVMIN. If GVMIN is not set, then thethrottle valves are still in positive control and the program computesthe throttle valve analog output as required by the speed controllervalue (SPD) and the ranging gain (GR6).

Eventually the state GVMIN will be set to indicate that the governorvalves are now in positive control. Then the throttle valve maximumposition state (TVMAX) is questioned. If it is not set, then thethrottle valve bias integrator (TVBIAS) is incremented by the biasconstant (BTVO) and the throttle valve analog output set accordingly. Ina short time the throttle valves are wide open; after this all logicalstates will be set to indicate this fact. Succeeding passes through theTHROTTLE VALVE CONTROL program will then hold the throttle valve analogoutputs wide open until the turbine is unlatched and tripped for somereason.

GOVERNOR VALVE CONTROL FUNCTION

The governor valve position, as set by the governor valve controlfunction, is compared to (and high limited by) the valve position limit(VPOSL) at all times. This gives the operator the ability to overridethe control system at any time that he considers it necessary, andallows him to control the position of the governor valves from VALVEPOSITION LIMIT RAISE and LOWER pushbuttons on the Operator's Panel. Ifthe governor valves are limited by the valve position limit (VPOSL), thelamp behind the VALVE POSITION LIMIT DISPLAY pushbutton flashes, thusalerting the operator to the condition.

Various logical numerical checks are necessary to determine which of thefive situations the turbine is currently in, on a second-by-second realtime basis. Further, the actual governor valve analog output computationis made for each of these five situations, along with the valve positionlimit checking feature and additional bookkeeping computations necessaryfor coordination of the various DEH programs.

Considering the flow chart of FIG. 43 at statement 1200, the valveposition limit state (VPLIM) is reset at each pass through the governorvalve control program. Then the governor control state (GC) isinterrogated; if it is not set, the throttle control state (TC) ischecked. If throttle control (TC) is not set, this means the turbine isunlatched and the governor valve minimum state (GVMIN) is checked. IfGVMIN is not set, then at statement 1270 all governor valve open statesare reset and all governor valve close states, including GVMIN, are set.The program then transfers to statement 1320 for analog outputcomputation and valve position limit checking to hold the governorvalves closed. Succeeding passes through the program will find the GVMINstate set and transfer directly to statement 1320.

If the turbine is latched, then the throttle control state (TC) is set.The governor valve control function finds itself at statement 1210,where the governor valve maximum state (GVMAX) is interrogated. If it isnot set, then the governor valve bias integrator (GVBIAS) is incrementedby the governor valve open-bias constant (BGVO), which is keyboardentered constant usually set at 10 percent to open the governor valvesincrementally when the turbine is latched. The program then transfers tostatement 1240 where the governor control state (GC) is again checked,since this point in the program may be reached from alternate paths. Forthe present situation, GC will not be set, thus leading to a check onwhether the governor valve bias integrator (GVBIAS) has reached 100percent and therefore have positioned the governor valves wide open.Assuming that GVBIAS has incremented up to 100 percent, all governorvalve close states are reset and all governor valve open states are set,including GVMAX. The program then transfers to statement 1320 for analogoutput computation and valve position limit checking to hold thegovernor valves wide open. Succeeding passes through the program findthe GVMAX state set at statement 1210 and transfer directly to statement1320.

Each of the cases discussed above apply when the governor control state(GC) is not set. Once the throttle/governor transfer is initiated,however, this sets the governor control state (GC), in which case theGOVERNOR VALVE CONTROL program arrives at statement 1220. The state ofthe breaker (BR) is checked; if BR is set, this means the DEH system ison load control and the program transfers to statement 1340 for loadcomputation of the governor valve analog outputs and valve positionlimit checking.

However, if the breaker (BR) is open and the DEH system still in speedcontrol, the check of BR at statement 1220 finds it not set. Then thethrottle/governor transfer complete state (TRCOM) is checked; assumingit has not yet been set, the governor valve closed state (GVMIN) ischecked. Normally this will not be set at this point in time, thusrequiring the governor valve bias integrator (GVBIAS) to be decrementedby the governor valve close-bias constant (BGVC), which is a keyboardentered quantity normally set at 100 percent to instantly close thegovernor valves when the transfer from throttle to governor control isinitiated.

The program then passes on to statement 1240 where the governor controlstate (GC) is checked again; since GC is set for the present discussion,then at statement 1260 the manual contact input (TM) is interrogated. Ifthe turbine is in manual control at this time, the program transfers tostatement 1270 for appropriate bookkeeping which will be describedshortly. If the turbine is in automatic control, then the test atstatement 1260 on the state of TM finds it not set and an additionaltest is made on whether the governor valve bias integrator (GVBIAS) hasreached zero to indicate the governor valves are closed. If it has not,then the program cycles through this area until the GVBIAS value iszero. Normally this will take only a few passes since the closing biasconstant (BGVC) will be quite large to achieve a fast, smooththrottle/governor valve transfer.

Once GVBIAS is zero, the GOVERNOR VALVE CONTROL program searches todetermine if the turbine speed (WS) has dropped below the speed attransfer WSTRANS by an amount WSDIP, which is a keyboard enteredconstant usually set at 10 rpm. When this has occurred, and assumingthat the analog backup system has followed the computer governor valveanalog output as indicated by the manual not tracking state (MANOTRAK)the GOVERNOR VALVE CONTROL program transfers to statement 1270. Allgovernor valve open states are reset and all governor valve closestates, including GVMIN, are set and the program passes on to statement1320 for computation of the governor valve analog output and valveposition limit checking to hold the governor valves closed.

The setting of GVMIN at statement 1270 leads to execution of the LOGICtask, which then uses this information to generate the throttle/governorvalve transfer complete state (TRCOM). Succeeding passes through theGOVERNOR VALVE CONTROL program at statement 1220 find TRCOM set andimmediately transfer to statement 1380 for computation of the governorvalve analog output and valve position limit checking to control turbinespeed. The portion of the program at statement 1320 is that necessary tohold the governor valves at the value residing in the governor valvebias integrator (GVBIAS).

The computations necessary to position the governor valves on loadcontrol determine where the load control governor valve set point (GVSP)lies with respect to a nonlinear curve which characterizes the governorvalve stroke mechanism. The result of this search positions GVSP alongthe abscissa of the curve, after which the actual valve position (GVPOS)is computed from analytical solution of points along the curve.

The computed governor valve position (GVPOS) is compared with thecurrent valve position limit (VPOSL). If GVPOS is below VPOSL, no actionis taken, if GVPOS is greater than VPOSL, then the valve positionlimiting state VPLIM is set, RUNLOGIC is set and the actual governorvalve position GVPOS is reset to the value residing in VPOSL. The LOGICand FLASH task perform their assigned functions of aligning the DEHsystem to these conditions and flashing the VALVE POSITION LIMIT DISPLAYlamp, respectively.

In the computations necessary to position the governor valves on speedcontrol, the speed controller percent output (SPD), suitably ratioed toaccount for differences between the speed ranging gain (GR7) and themaximum ranging factor of 20.47, is checked against the current valveposition limit (VPOSL). If the ratioed speed controller output is belowVPOSL, no special action is taken; if VPOSL is violated, then the valveposition limiting states (VPLIM and RUNLOGIC) are set to trigger theappropriate responses from the LOGIC and FLASH tasks. In addition thespeed controller output (SPD) and the speed integrator (RESSPD) arereset to values consistent with VPOSL.

A FORTRAN DO loop is executed to make final checks on both the throttleand governor valve analog outputs. They are low-limit-checked toguarantee that they do not go below zero and high-limit-checked toguarantee that they do not go above the maximum analog output voltagepattern. Then, the analog output handler is called to output thecomputed throttle and governor valve patterns. Finally, the CONTROL taskexits to the Monitor for the next bid 1 sec later.

CCI SCAN MONITOR -- ANNUNCIATOR ALARM

The DEH system scans contact inputs on a demand basis. The scan isinitiated by a change of state of any contact. This change triggers asequence of events interrupt which in turn bids the CONTACT SCANprogram. However under certain conditions such as may occur duringinitial plant startup when all wiring has not been completely checkedout, high-frequency noise on a contact can result in the sequenceinterrupt being generated continuously. This activity essentially"captures" the computer and prevents the DEH programs from carrying outtheir normal functions.

In order to counteract such a condition, special logic detectshigh-frequency contact noise. Should this occur, the DEH systemimmediately switches from a demand scan to a 1/2 sec periodic contactscan, the sequence interrupt is disabled, and a contact output is setwhich triggers the DEH CCI SCAN MONITOR annunciator alarm. If thishappens, the noisy contact input should be found and the field problemfixed. After this is done, the DEH system may be returned to itsoriginally designed demand scan by entering a particular constant fromthe keyboard as follows:

1. Turn the MAINTENANCE TEST key to the TEST position; this switches theturbine to manual control.

2. Press the PROGRAM DISPLAY button, which then back-lights.

3. Key in the address 3141 and press the ENTER buttons. The addressappears in the left windows and the value 1.000 appears in the rightwindows.

4. Press the CHANGE button, which backlights. The right windows clear tozero.

5. Key in the value 0 and press the ENTER button. The CHANGE lamp goesout and the DEH CCI SCAN MONITOR annunciator is turned off.

6. Return the MAINTENANCE TEST key to the OFF position. The DEH systemtracks the manual backup system preparatory to transfer to automaticcontrol, which the normal demand scan being used.

I claim:
 1. A system for operating a steam turbine in an electric powerplant, said system comprising an arrangement of throttle and governorvalves for supplying steam to the turbine, means for actuating saidvalves to position said valves in accordance with valve positionsignals, means for generating signals representative of the turbinespeed and the turbine load and other turbine variables, a digitalcontroller having means for generating a speed setpoint and means forgenerating a load setpoint, means for coupling the turbine speed andload signals and the other turbine variable signals to said digitalcontroller on a periodic or demand basis, means for registering thecoupled speed and load and other turbine variables in said digitalcontroller, said digital controller including a speed control forperiodically generating valve position outputs in response to theturbine speed and speed setpoint during turbine startup, said digitalcontroller further including a load control for periodically generatingvalve position outputs in response to the turbine load and load setpointduring turbine load operation, means for continuously generating thevalve position signals in response to the valve position outputs, saidcoupling means including means for generating contact signalsrepresentative of predetermined turbine variables and for scanning suchsignals on a predetermined basis for registration in said digitalcontroller, said coupling means further including means for convertinginput analog signals to digital signals and for periodically scanningthe digital signals for registration in said digital controller, anoperator panel having switching means for generating control mode andcontrol parameter signals, means for coupling the operator panel signalsto said digital controller and for registering such signals in saiddigital controller, said speed and load controls having a plurality ofcontrol elements and mode switching means for determining which elementsare operative in the functioning of the controls, a logic control forgenerating mode control outputs for operating said mode switching meansin response to the registered control mode panel signals and theregistered turbine contact signals, said digital controller includingmeans for generating synchronous outputs to trigger the operation ofsaid speed and load controls on a periodic basis, and means foroperating said logic control on demand in response to changes in thepanel or turbine contact signals.
 2. A steam turbine operating system asset forth in claim 1 wherein said digital controller is embodied with adigital computer which further includes monitor means for controllingthe execution of said logic control and said speed and load controls andother predetermined program elements in response to program run bids andin accordance with a predetermined priority system.
 3. A steam turbineoperating system as set forth in claim 2 wherein said synchronousgenerator output means includes an auxiliary synchronizer whichgenerates trigger outputs for speed and load control program executionfor which periodic bids are placed for its own execution at a ratesubstantially more frequent than the rate at which the control programis to be executed, said monitor means placing a higher priority onexecution of said auxiliary synchronizer than on said speed and loadcontrols.
 4. A steam turbine operating system as set forth in claim 3wherein bids are placed for execution of said logic control on demandand said monitor means places a higher priority on control programexecution than on logic control program execution.
 5. A steam turbineoperating system as set forth in claim 3 wherein said auxiliarysynchronizer further generates trigger outputs for said analog scan at arate faster than the execution rate for said speed and load controls andslower than the auxiliary synchronizer execution rate, and wherein saidmonitor means places priorities on execution bids in the other auxiliarysynchronizer, speed and load control, analog scan and logic control. 6.A steam turbine operating system as set forth in claim 2 wherein saidsynchronous generator output means includes an auxiliary synchronizerwhich generates trigger outputs for operating said periodic analogscanning means and for which periodic bids are placed for its ownexecution at a rate substantially more frequent than the rate at whichthe analog scan is to be executed, said monitor means placing a higherpriority on execution of said auxiliary synchronizer than on said analogmeans.
 7. A steam turbine operating system as set forth in claim 2wherein the input contact signals are normally scanned on demandinitiated by a contact signal change wherein said computer includesmeans for scanning the input contact signals periodically if computerduty above a predetermined level is being applied to contact scanning ona demand basis.
 8. A steam turbine operating system as set forth inclaim 1 wherein the input contact signals are normally scanned on demandinitiated by a contact signal change.
 9. A steam turbine operatingsystem as set forth in claim 1 wherein said speed and load controlfunctions approximately once each second and said analog scanning meansfunctions approximately once each half second.
 10. A steam turbineoperating system as set forth in claim 1 wherein said speed and loadcontrols include a proportional plus reset controller, means forcoupling said porportional plus reset controller to each of said controlelements which require a proportional plus reset function when suchcontrol elements are to be operated, means for uncoupling saidproportional plus reset controller for each of the latter controlelements when an output has been provided for each of such controlelements, and means for registering the outputs from said proportionalplus reset controller for use in the operation of the speed and loadconcontrols.
 11. A steam turbine operating system as set forth in claim1 wherein a speed controller is provided for generating a characteristicoutput in response to speed error, and means are provided for couplingsaid speed controller in said speed control or said load controlaccording to the control mode.
 12. A steam turbine operating system asset forth in claim 11 wherein the speed controller is a proportionalplus integral controller and said speed controller coupling meansincludes means for applying one characterization in speed control andanother characterization in load control.
 13. A system for operating asteam turbine in an electric power plant, said system comprising anarrangement of throttle and governor valves for supplying stream to theturbine, means for actuating said valves to position said valves inaccordance with valve position signals, means for generating signalsrepresentative of the turbine speed and the turbine load and otherturbine variables, a digital controller having means for generating aspeed setpoint and means for generating a load setpoint, means forcoupling the turbine speed and load signals and the other turbinevariable signals to said digital controller on a periodic or demandbasis, means for registering the coupled speed and load and otherturbine variables in said digital controller, said digital controllerincluding a speed control for periodically generating valve positionoutputs in response to the turbine speed and speed setpoint duringturbine startup, said digital controller further including a loadcontrol for periodically generating valve position outputs in responseto the turbine load and load setpoint during turbine load operation,means for continuously generating the valve position signals in responseto the valve position outputs, said coupling means including means forgenerating contact signals representative of predetermined turbinevariables and for scanning such signals on a predetermined basis forregistration in said digital controller, said coupling means furtherincluding means for converting input analog signals to digital signalsand for periodically scanning the digital signals for registration insaid digital controller, an operator panel having switching means forgenerating control mode and control parameter signals, means forcoupling the operator panel signals to said digital controller and forregistering such signals in said digital controller, said speed and loadcontrols having a plurality of control elements and mode switching meansfor determining which elements are operative in the functioning of thecontrols, means for controlling said mode switching means in response tothe registered control mode panel signals and the registered turbinecontact signals, a flip-flop for generating switch outputs, means forconnecting said flip-flop at least into said load and speed controls tofunction as each of at least some of said mode switching means and togenerate a switch output for registration and speed and load controloperation when so connected.
 14. A system for operating a steam turbinein an electric power plant, said system comprising an arrangement ofthrottle and governor valves for supplying steam to the turbine, meansfor actuating said valves to position said valves in accordance withvalve position signals, means for generating signals representative ofthe turbine speed and the turbine load and other turbine variables, adigital controller having means for generating a speed setpoint andmeans for generating a load setpoint, means for coupling the turbinespeed and load signals and the other turbine variable signals to saiddigital controller on a periodic or demand basis, means for registeringthe coupled speed and load and other turbine variables in said digitalcontroller, said digital controller including a speed control forperiodically generating valve position outputs in response to theturbine speed and speed setpoint during turbine startup, said digitalcontroller further including a load control for periodically generatingvalve position outputs in response to the turbine load and load setpointduring turbine load operation, means for continuously generating thevalve position signals in response to the valve position outputs, saidcoupling means including means for generating contact signalsrepresentative of predetermined turbine variables and for scanning suchsignals on a predetermined basis for registration in said digitalcontroller, said coupling means further including means for convertinginput analog signals to digital signals and for periodically scanningthe digital signals for registration in said digital controller, anoperator panel having switching means for generating control mode andcontrol parameter signals, means for coupling the operator panel signalsto said digital controller and for registering such signals in saiddigital controller, said speed and load controls having a plurality ofcontrol elements and mode switching means for determining which elementsare operative in the functioning of the controls, means for controllingsaid mode switching means in response to the registered control modepanel signals and the registered turbine contact signals, said digitalcontroller being embodied with a digital computer having monitor meansfor controlling the execution of said speed and load controls and otherpredetermined program elements in response to program run bids and inaccordance with a predetermined priority system said synchronousgenerator output means including an auxiliary synchronizer whichgenerates trigger outputs for speed and load control program executionfor which periodic bids are placed for its own execution at a ratesubstantially more frequent than the rate at which the control programis to be executed, said monitor means placing a higher priority onexecution of said auxiliary synchronizer than on said speed and loadcontrols.
 15. A steam turbine operating system as set forth in claim 14wherein said auxiliary synchronizer also triggers said analog scan meansat a rate faster than the execution rate for said speed and loadcontrols and slower than the auxiliary synchronizer execution rate andwherein said monitor means places priorities on execution bids in theother auxiliary synchronizer, speed and load control, and analog scan.16. A system for operating a steam turbine in an electric power plant,said system comprising an arrangement of throttle and governor valvesfor supplying steam to the turbine, means for actuating said valves toposition said valves in accordance with valve position signals, meansfor generating signals representative of the turbine speed and theturbine load and other turbine variables, a digital controller havingmeans for generating a speed setpoint and means for generating a loadsetpoint, means for coupling the turbine speed and load signals and theother turbine variable signals to said digital controller on a periodicor demand basis, means for registering the coupled speed and load andother turbine variables in said digital controller, said digitalcontroller including a speed control for periodically generating valveposition outputs in response to the turbine speed and speed setpointduring turbine startup, said digital controller further including a loadcontrol for periodically generating valve position outputs in responseto the turbine load and load setpoint during turbine load operation,means for continuously generating the valve position signals in responseto the valve position outputs, said coupling means including means forgenerating contact signals representative of predetermined turbinevariables and for scanning such signals on a predetermined basis forregistration in said digital controller, said coupling means furtherincluding means for converting input analog signals to digital signalsand for periodically scanning the digital signals for registration insaid digital controller, an operator panel having switching means forgenerating control mode and control parameter signals, means forcoupling the operator panel signals to said digital controller and forregistering such signals in said digital controller, said speed and loadcontrols having a plurality of control elements and mode switching meansfor determining which elements are operative in the functioning of thecontrols, means for controlling said mode switching means in response tothe registered control mode panel signals and the registered turbinecontact signals, said speed and load controls including a proportionalplus reset controller means for coupling said proportional plus resetcontroller to each of said control elements which require a proportionalplus reset function when such contact elements are to be operated, meansfor uncoupling said proportional plus reset controller from each of thelatter control elements when an output has been provided for each ofsuch control elements, and means for registering the outputs from saidproportional plus reset control for use in other operation of the speedand load controls.